B757 / B767 PRM Breakout Manoever

B757 / B767 Non-Recall Limitations

B757 / B767 Recall Limitations

B757 / B767 Memory Items

B757 / B767 Simulator Prep

4.14 FCT 757/767 (TM)

Engine Inoperative Cruise/Driftdown

Engine Inoperative Cruise/Driftdown

Execution of a non-normal checklist or sudden engine failure may lead to the

requirement to perform an engine inoperative driftdown and diversion to an

alternate airport. Engine inoperative cruise information is available from the

FMC. An analysis of diversion airport options is available using the FMC ALTN

page (as installed).

If an engine failure occurs while at cruise altitude, it may be necessary to descend.

The autothrottle should be disconnected, thrust reference set to CON and the

thrust manually set to MCT on the operative engine. On the FMC ACT CRZ page,

select the ENG OUT. This displays MOD CRZ calculated on engine out MCT and

maintaining the airspeed displayed on the EO SPD line.

Set the engine out cruise altitude in the MCP altitude window and execute the

ENG OUT CRZ D/D page. The thrust reference mode on the EICAS display will

display CON. The airplane descends in VNAV using the VNAV SPD pitch mode.

Once the descent rate has decreased to 300 fpm during driftdown it is held

constant by the FMC until altitude capture.

At altitude capture the ENG OUT CRZ page is displayed. Maintain MCT on the

operative engine and driftdown altitude until the E/O SPD speed is established.

Maintain this speed using manual thrust adjustments.

After level off at the target altitude, maintain MCT and allow the airplane to

accelerate to the single engine long range cruise speed. Maintain this speed with

manual thrust adjustments. Entering the new cruise altitude and airspeed on the

ECON CRZ page updates the ETAs and Top of Descent predictions. When the

ENG OUT VNAV mode is selected and an engine-out condition is detected, the

FMC computes engine-out trip predictions, guidance parameters, and MAX ALT

consistent with the detected engine-out conditions, the selected thrust rating using

the actual bleeds. Refer to Engine Out Familiarization, chapter 7, for trim

techniques.

If required to cruise at maximum altitude, set MCT, establish a climb and

decelerate slowly to ENG OUT CRZ speed. At level off select ENG OUT LRC

for best fuel economy.

An alternate target driftdown speed can be selected using the MOD CRZ or ENG

OUT D/D page. LRC speed would result in a lower driftdown altitude but better

fuel performance. A company specified speed could be selected and provides for

a higher driftdown speed and a shorter flight time to the alternate.

An ENG OUT ALT can be entered on the MOD CRZ or ENG OUT D/D page. If

an engine out cruise altitude lower than the computed maximum altitude is

entered, the FMC commands a cruise descent at approximately 1250 fpm rather

than a driftdown schedule.

Unless altered by the pilot, the level off cruise mode will be the same as was used

during driftdown. FMC fuel and ETA calculations for driftdown and the

remainder of the trip will be consistent with the selected speed mode. For best fuel

performance select the engine-out LRC mode following a minimum drag speed

(E/O) driftdown.

When VNAV is not used during engine out, set MCT on the operative engine and

maintain altitude until the airplane decelerates to the displayed appropriate engine

out speed. Use engine out speed from the FMC while descending to the engine out

cruise altitude. Remain at MCT until the airplane accelerates to LRC, then

maintain LRC speed with manual thrust adjustments. If the FMC is inoperative

use turbulence penetration airspeed to driftdown and the engine out long-range cruise tables in the QRH.

Aerodynamic Principles of Large-Airplane Upsets -Boeing

To our readers:
Loss of airplane control in flight is a leading cause of fatalities in the commercial aviation industry. A variety of reasons exist for airplane upsets, but none is statistically significant. Reducing the number of reasons for upsets is a continual training process, and eliminating one reason will not necessarily reduce the number of loss-of-control accidents and fatalities. Additionally, many reasons for upsets are associated with the environment, in which case avoidance is the best solution, but is not always possible. Therefore, pilots must have the necessary knowledge and skills to recover an upset airplane.
Aerodynamic principles of large, swept-wing commercial jet airplanes are similar among all manufacturers. In the interest of safety, and the desire to acknowledge the commonality in recovery techniques, this article was written jointly by Airbus, Boeing Commercial Airplane Group, and Douglas Products Division. The article focuses on Airbus and Boeing airplanes that do not have electronic flight controls, commonly known as fly-by-wire. However, when a fly-by-wire airplane is in a degraded control law (mode), the recovery techniques are appropriate. Additionally, certain conditions can upset any airplane and the basic principles of recognition and recovery still apply regardless of the flight control architecture.
Pilots can be exposed to an infinite number of slightly different situations. For this reason, it is not possible to develop specific recovery procedures for each. Operators should address procedural application of techniques within their fleet structures. Pilots who are knowledgeable about aerodynamics and who possess the skills to apply basic recovery techniques can return an upset airplane to normal flight parameters. Airbus and Boeing are dedicating many resources and actively working with an industry team to develop an airplane upset recovery training aid. When it is completed we will make it available to our customers at no charge.
Airline flight crews constantly strive to provide passengers with a smooth ride while ensuring an extremely high degree of safety. Pilots in line operation seldom experience the excessive pitch or bank angles associated with an airplane upset. However, with a greater understanding of the fundamental principles of aerodynamics, pilots will be better equipped to successfully maneuver the airplane back to straight-and-level flight in the unlikely event they experience an airplane upset.
Aerodynamic principles applied to large, swept-wing commercial jet airplanes are similar among all manufacturers, and the recommended techniques for recovering from an upset in an airplane subject to these principles are also compatible. Pilots who understand the conditions of an upset, though such an event is unlikely, will be better prepared to recover from it. The four conditions that generally describe an airplane upset (figure 1) are unintentional:

• Pitch attitude more than 25 degrees nose up.
• Pitch attitude more than 10 degrees nose down.
• Bank angle more than 45 degrees.
• Flight within these parameters at airspeeds inappropriate for the conditions.

In order to avoid an upset, or to recover from one, pilots must understand the following:

• 1. Aerodynamic fundamentals applied to large airplanes.
• 2. Application of aerodynamic fundamentals to airplane upsets.
• 3. Recovery techniques.

Aerodynamic Fundamentals Applied to Large Airplanes
Airline pilots are thoroughly familiar with airplane handling qualities under normal flight conditions. In general, if pitch is increased (the result of pulling back on the controls), altitude increases; in level flight, if thrust is increased, airspeed increases.
However, when an airplane is taken to the edges of the flight envelope, different situations result. It is possible, for example, to encounter flight conditions where an increase in thrust is needed to maintain a slower airspeed, and where an increase in pitch will decrease altitude. While airline pilots may have received training on how to use flight controls to recover from airplane upsets, they rarely, if ever, experience these conditions in line operations.
In the context of aerodynamics, the following three basic concepts should be understood:

• Energy management.
• Pitch control.
• Lateral and directional control.

ENERGY MANAGEMENT.
Three sources of energy are available to generate aerodynamic forces and thus maneuver the airplane: kinetic, which increases with increasing airspeed; potential, which is proportional to altitude; and chemical, which is from the fuel in the airplane's tanks. The term "energy state" describes how much of each kind of energy the airplane has available at any given time. The critical element to realize is that pilots who understand the airplane energy state will be in a position to know what options are available to maneuver the airplane.
The airplane is continuously expending energy in flight because of drag. Drag is usually offset by using some of the stored chemical energy -- that is, by burning fuel in the engines. (At landing, the reverse is the case when wheel brakes [friction] and thrust reversers dissipate energy.)
During maneuvering, the three types of energy can be traded, or exchanged, usually at the cost of additional drag. This process of consciously manipulating the energy state of the airplane is referred to as energy management. Airspeed (kinetic energy) can be traded for altitude (potential energy). Altitude therefore can be traded for airspeed, as in a dive. This trading of energy, however, must be balanced with the final desired energy state in mind. For example, when a pilot trades altitude for airspeed by descending the airplane, the descent angle must be selected carefully in order to capture the final desired energy state with the introduction of the necessary chemical energy.
This becomes especially important when the pilot wants to generate aerodynamic forces and moments to maneuver the airplane. Kinetic energy can be traded for potential energy (climb). Potential energy can be converted to kinetic energy. Chemical energy can be converted by engines to either potential or kinetic energy, but only at specified rates. These relationships are shown in figure 2.
The objective of maneuvering the airplane is to manage energy so that kinetic energy stays between limits (stall and placards), potential energy stays within limits (terrain-to-buffet altitude), and chemical energy stays above certain thresholds (fuel in tanks). These concepts are especially important to understanding recovery from an airplane upset.
In managing these energy states and trading between the sources of energy, the pilot does not directly control the energy. The pilot controls the direction and magnitude of the forces acting on the airplane. These forces result in accelerations applied to the airplane. The result of these accelerations is a change in the orientation of the airplane and a change in the direction, magnitude, or both, of the flight path vector. Ultimately, velocity and altitude define the energy state.
This process of controlling forces to change accelerations and produce a new energy state takes time. The amount of time required is a function of the mass of the airplane and the magnitude of the applied forces, and is governed by Newton's laws. Airplanes of larger mass generally take longer to change orientation than do smaller ones. This longer time requires the pilot to plan ahead in a large-mass airplane to ensure that the actions taken will result in the final desired energy state.
Thrust, weight, lift, and drag are the forces that act upon an airplane (figure 3). Maneuvering is accomplished by variations of these forces and is controlled by the throttles and flight controls.
The lift force in pounds or kilograms generated by a surface is a result of the angle of attack, the dynamic pressure of the air moving around it (which is a function of the airspeed and density), and the size and shape of the surface. Lift varies with angle of attack for constant speed and air density. As angle of attack is increased, the lift increases proportionally, and this increase in lift is normally linear. At a specific angle of attack, however, the resulting lift due to angle of attack behaves differently. Instead of increasing, it decreases. At this critical angle of attack, the air moving over the upper wing surface can no longer remain attached to the surface, the flow breaks down, and the surface is considered stalled. The breakdown of the flow and consequent loss of lift is dependent only upon the angle of attack of the surface. This is true regardless of airplane speed or attitude. An airplane stall is characterized by any one (or a combination) of the following conditions:

• Buffeting.
• Lack of pitch authority.
• Lack of roll control.
• Inability to arrest descent rate.

These conditions are usually accompanied by a continuous stall warning. A stall must not be confused with the stall warning that alerts the pilot to an approaching stall. Recovery from an approach to stall is not the same as a recovery from an actual stall. An approach to stall is a controlled flight maneuver; a stall is an out-of-control, but recoverable, condition.
Flight controls give the pilot the ability to manage the forces acting on the airplane in order to maneuver; that is, to change the flight path of the airplane (figure 4).

PITCH CONTROL.
Movement around the lateral axis of an airplane is called pitch (figure 5), and is usually controlled by the elevator. Given any specific combination of airplane configuration, weight, center of gravity, and speed, all forces will be balanced at one elevator position. In flight, the two elements most easily changed are speed and elevator position; as speed changes, the elevator position must be adjusted to balance the aerodynamic forces. Control forces required for this new position can be neutralized by adjusting the pitch trim mechanism. Typically, the pitch trim mechanism adjusts the position of the horizontal stabilizer.
An important concept for pilots to understand is that if the airplane is at a balanced, "in-trim" angle of attack in flight, it will generally seek to return to the trimmed angle of attack if upset by external forces or momentary pilot input. This is due to the longitudinal stability designed into that airplane.
Changes in airplane configuration also affect pitch control. For example, flap extension usually creates a nose-down pitching moment; flap retraction usually creates a nose-up pitch. When extended, wing-mounted speed brakes usually produce a nose-up pitching moment.
Pitch attitude can also change with thrust (figure 5). With underwing engines, reducing thrust creates a nose-down pitching moment; increasing thrust creates a nose-up pitching moment. The combination of elevator and stabilizer positions also affects pitch. In normal maneuvering, the pilot displaces the elevator by applying an elevator control force. The pilot then trims the stabilizer by driving it to a new position to remove the elevator control force. This new stabilizer position is faired with the elevator. If they are not faired (one is down and the other is up), one cancels out the other. This condition limits the airplane's ability to overcome other pitching moments from configuration changes or thrust.

LATERAL AND DIRECTIONAL CONTROL.
Similar to how feathers on the back of an arrow make it fly straight, airplanes have a vertical stabilizer to keep the nose into the wind. The rudder is attached to the vertical stabilizer, and movement of the rudder into the airflow creates a force and a resulting rotation about the vertical axis. This motion is called yaw (figure 5). The vertical stabilizer and the rudder are sized to meet two objectives: to control asymmetric thrust from an engine failure at the most demanding flight condition (greater than V₁), and to generate sufficient sideslip for crosswind landings. To achieve these objectives, the vertical stabilizer and rudder must be capable of generating powerful yawing moments and large sideslip angles.
Motion about the longitudinal axis is called roll (figure 5). Control inputs cause the ailerons and spoilers to control the airplane's roll rate. The aileron and spoiler movement changes the local angle of attack of the wing, changing the amount of lift and causing rotation about the longitudinal axis.
During an airplane upset, unusually large amounts of aileron or spoiler input may be required to recover the airplane. After input of full roll control, it may be necessary to use rudder in the direction of the desired roll. The amount of rudder required to coordinate the maneuver will depend on the airplane type and associated systems. An uncoordinated rudder movement results in a nose movement (yaw) in the direction of the rudder input. The yaw creates sideslip, which causes a roll in the same direction as the rudder input. The roll due to sideslip is referred to as dihedral effect.
When encountering an angle of attack associated with the onset of stick shaker, ailerons and spoilers are still effective at controlling roll. However, as the angle of attack continues to increase beyond the angle associated with stick shaker onset, the airflow over the wing separates and airplane buffet generally begins. Without decreasing the angle of attack, the combination of ailerons and spoilers in this separated airflow may not always generate a significant force; therefore, little rotation about the longitudinal axis occurs on some models. Since the vertical stabilizer/rudder is rarely aerodynamically stalled, it is still possible to generate a force and a nose rotation with associated roll rate.
However, at a high angle of attack, pilots must be extremely careful when using the rudder for assisting lateral control. Excessive rudder can cause excessive sideslip which could lead to departure from controlled flight.
Asymmetric thrust creates a yawing and a rolling moment. An engine failure creates an undesired yaw and roll. Conversely, an intentional engine throttle up or down could create a desired yawing moment followed by a desired rolling moment. Using asymmetric thrust to control roll is not precise because of the lag time associated with engine spool-up or spool-down and should be avoided unless no other means of roll control are available. Generally, the pilot should attempt to restore symmetric thrust conditions during an upset recovery.
Applying Aerodynamic Fundamentals to Airplane Upsets
Though airline pilots in line operation will rarely, if ever, encounter an upset situation, understanding how to apply aerodynamic fundamentals in such a situation will help them control the airplane. Several techniques are available for recovering from an upset. In most situations, if a technique is effective, it is not recommended that pilots use additional techniques. Several of these techniques are discussed in the example scenarios below:

• Stall recovery.
• Nose high, wings level.
• Nose low, wings level.
• High bank angles.

STALL RECOVERY.
In all upset situations, it is necessary to recover from a stall before applying any other recovery actions. To recover from the stall, angle of attack must be reduced below the stalling angle. Nose-down pitch control must be applied and maintained until the wings are unstalled. Under certain conditions, on airplanes with underwing-mounted engines, it may be necessary to reduce some thrust in order to prevent the angle of attack from continuing to increase. Once unstalled, upset recovery actions may be taken and thrust reapplied as needed.
NOSE HIGH, WINGS LEVEL.
In a situation where the airplane pitch attitude is unintentionally more than 25 degrees nose high and increasing, the kinetic energy (airspeed) is decreasing rapidly. According to the energy management discussed earlier, the energy is actually being stored as potential energy. As airspeed decreases, the pilot's ability to maneuver the airplane also decreases. If the stabilizer trim setting is nose up, as for slow-speed flight, it partially reduces the nose-down authority of the elevator. Further complicating this situation, as the airspeed decreases, the pilot could intuitively make a large thrust increase. This will cause an additional pitch up for underwing-mounted engines. At full thrust settings and very low airspeeds, the elevator -- working in opposition to the stabilizer -- will have limited control to reduce the pitch attitude.
In this situation the pilot should trade the potential energy of altitude for airspeed, and would have to maneuver the airplane's flight path back toward the horizon. This is accomplished by the input of up to full nose-down elevator and the use of some nose-down stabilizer trim. These actions should provide sufficient elevator control power to produce a nose-down pitch rate. It may be difficult to know how much stabilizer trim to use, and care must be taken to avoid using too much trim. Pilots should not fly the airplane using stabilizer trim, and should stop trimming nose down when they feel the g force on the airplane lessen or the required elevator force lessen. This use of stabilizer trim may correct an out-of-trim airplane and solve a less-critical problem before the pilot must apply further recovery measures. Because a large nose-down pitch rate will result in a condition of less than 1 g, at this point the pitch rate should be controlled by modifying control inputs to maintain between 0 to 1 g. If altitude permits, flight tests have determined that an effective way to achieve a nose-down pitch rate is to reduce some thrust on airplanes with underwing-mounted engines. The use of this technique is not intuitive and must be considered by each operator for their specific fleet types.
If normal pitch control inputs do not stop an increasing pitch rate, rolling the airplane to a bank angle that starts the nose down should work. Bank angles of about 45 degrees, up to a maximum of 60 degrees, could be needed. Unloading the wing by maintaining continuous nose-down elevator pressure will keep the wing angle of attack as low as possible, making the normal roll controls as effective as possible. With airspeed as low as stick shaker onset, normal roll controls -- up to full deflection of ailerons and spoilers -- may be used. The rolling maneuver changes the pitch rate into a turning maneuver, allowing the pitch to decrease. Finally, if normal pitch control then roll control is ineffective, careful rudder input in the direction of the desired roll may be required to induce a rolling maneuver for recovery.
Only a small amount of rudder is needed. Too much rudder applied too quickly or held too long may result in loss of lateral and directional control. Because of the low energy condition, pilots should exercise caution when applying rudder.
The reduced pitch attitude will allow airspeed to increase, thereby improving elevator and aileron control effectiveness. After the pitch attitude and airspeed return to a desired range the pilot can reduce angle of bank with normal lateral flight controls and return the airplane to normal flight.
NOSE LOW, WINGS LEVEL.
In a situation where the airplane pitch attitude is unintentionally more than 10 degrees nose low and going lower, the kinetic energy (airspeed) is increasing rapidly. A pilot would likely reduce thrust and extend the speed brakes. The thrust reduction will cause an additional nose-down pitching moment. The speed brake extension will cause a nose-up pitching moment, an increase in drag, and a decrease in lift for the same angle of attack. At airspeeds well above V_MO/M_MO, the ability to command a nose-up pitch rate with elevator may be reduced because of the extreme aero-dynamic loads on the elevator.
Again, it is necessary to maneuver the airplane's flight path back toward the horizon. At moderate pitch attitudes, applying nose-up elevator -- and reducing thrust and extending speed brakes, if necessary -- will change the pitch attitude to a desired range. At extremely low pitch attitudes and high airspeeds (well above V_MO/M_MO), nose-up elevator and nose-up trim may be required to establish a nose-up pitch rate.
HIGH BANK ANGLES.
A high bank angle is one beyond that necessary for normal flight. Though the bank angle for an upset has been defined as unintentionally more than 45 degrees, it is possible to experience bank angles greater than 90 degrees.
Any time the airplane is not in "zero-angle-of-bank" flight, lift created by the wings is not being fully applied against gravity, and more than 1 g will be required for level flight (figure 6). At bank angles greater than 67 degrees, level flight cannot be maintained within flight manual limits for a 2.5 g load factor (figure 7). In high bank angle increasing airspeed situations, the primary objective is to maneuver the lift of the airplane to directly oppose the force of gravity by rolling to wings level. Applying nose-up elevator at bank angles above 60 degrees causes no appreciable change in pitch attitude and may exceed normal structure load limits as well as the wing angle of attack for stall. The closer the lift vector is to vertical (wings level), the more effective the applied g is in recovering the airplane.
A smooth application of up to full lateral control should provide enough roll control power to establish a very positive recovery roll rate. If full roll control application is not satisfactory, it may even be necessary to apply some rudder in the direction of the desired roll.
Only a small amount of rudder is needed. Too much rudder applied too quickly or held too long may result in loss of lateral and directional control or structural failure.
NOSE HIGH, HIGH BANK ANGLES.
A nose-high, high-angle-of-bank upset requires deliberate flight control inputs. A large bank angle is helpful in reducing excessively high pitch attitudes. The pilot must apply nose-down elevator and adjust the bank angle to achieve the desired rate of pitch reduction while considering energy management. Once the pitch attitude has been reduced to the desired level, it is necessary only to reduce the bank angle, ensure that sufficient airspeed has been achieved, and return the airplane to level flight.
NOSE LOW, HIGH BANK ANGLES.
The nose-low, high-angle-of-bank upset requires prompt action by the pilot as potential energy (altitude) is rapidly being exchanged for kinetic energy (airspeed). Even if the airplane is at a high enough altitude that ground impact is not an immediate concern, airspeed can rapidly increase beyond airplane design limits. Simultaneous application of roll and adjustment of thrust may be necessary. It may be necessary to apply nose-down elevator to limit the amount of lift, which will be acting toward the ground if the bank angle exceeds 90 degrees. This will also reduce wing angle of attack to improve roll capability. Full aileron and spoiler input should be used if necessary to smoothly establish a recovery roll rate toward the nearest horizon. It is important to not increase g force or use nose-up elevator or stabilizer until approaching wings level. The pilot should also extend the speed brakes as necessary.
Recovery Techniques
It is possible to consolidate and incorporate recovery techniques into two basic scenarios -- nose-high and nose-low -- and to acknowledge the potential for high bank angles in each scenario described above. Other crew actions such as recognizing the upset, reducing automation, and completing the recovery are included in these techniques. Boeing and Airbus believe the recommended techniques provide a logical progression for recovering an airplane. The techniques assume that the airplane is not stalled. If it is, recovery from the stall must be accomplished first.
NOSE-HIGH RECOVERY

• Recognize and confirm the situation.
• Disengage autopilot and autothrottle.
• Apply as much as full nose-down elevator.
• Apply appropriate nose-down stabilizer trim.
• Reduce thrust (for underwing-mounted engines).
• Roll (adjust bank angle) to obtain a nose-down pitch rate.
• Complete the recovery:
  ÐWhen approaching the horizon, roll to wings level.
  ÐCheck airspeed and adjust thrust.
  ÐEstablish pitch attitude.

NOSE-LOW RECOVERY

• Recognize and confirm the situation.
• Disengage autopilot and autothrottle.
• Recover from stall, if necessary.
• Roll in the shortest direction to wings level (unload and roll if bank angle is more than 90 degrees).
• Recover to level flight:
  Ð Apply nose-up elevator.
  Ð Apply stabilizer trim, if necessary.
  Ð Adjust thrust and drag as necessary.

Summary
Airplanes are subject to the laws of aerodynamics and physics. With a clear understanding of how airplanes react when obeying these laws, pilots will be better equipped to safely deal with an airplane upset in the rare event that one occurs. Each upset event may result from different causes, but the concepts for recovery are similar.

• Assess the energy situation.
• Understand where the ground is.
• Use whatever authority is required of the flight controls.
• Maneuver the airplane to return to normal bank and pitch.

These recovery concepts are central to any upset training. To help pilots develop a greater understanding of upset recovery procedures, the commercial aviation industry is developing an upset recovery training program. A training aid representing an industry consensus on a core training program was scheduled to be completed in second-quarter 1998 and delivered to operators of Airbus and Boeing airplanes beginning in third-quarter 1998. It is anticipated that this training aid will be an important factor in enhancing aviation safety by reducing loss-of-control events and the accidents that may result from them.


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Airplane Upset Recovery Training Aid
In recent years the commercial aviation industry has responded to flight crew training issues by developing several training aids. Examples of these aids, which were created by industry teams of representatives from airplane manufacturers, airlines, pilot groups, government and regulatory agencies, and others, include the following:

• Controlled flight into terrain.
• Takeoff safety.
• Turbulence.
• Turbulence avoidance.
• Windshear.

The industry has now identified the potential benefits of such a training aid to help pilots recover an airplane that has been upset. The goal of this airplane upset recovery training aid is to increase the pilot's ability to recognize and avoid situations that can lead to airplane upsets, and to improve the pilot's ability to recover control of an airplane to normal flight parameters if it has been upset. To support this goal the industry:

• Established an industrywide consensus on a variety of effective methods to train pilots to recover from airplane upsets.
• Developed appropriate educational material.
• Developed an example training program as a basis for tailored programs that individual operators may wish to develop.

The new training aid package consists of a document and a two-part video. Both the document and video will also be available in CD-ROM format. The document contains four sections:
1. A management overview that identifies the safety concern and encourages operators to establish an upset recovery training program.
2. A pilot guide that briefly reviews the causes of airplane upsets, fundamental aerodynamics of flight for large, swept-wing airplanes, and the application of techniques for recovering an airplane that has been upset. The guide is a highly readable, concise treatment for pilot issues written by pilots for pilots. It is intended for self-study or classroom use.
3. The example airplane upset training program, a stand-alone resource designed to serve the needs of a training department. An example academic and simulator training program are both included. The academic program provides the pilots with the requisite knowledge, and the simulator training scenarios are designed to help pilots improve their skills in recovering from an upset.
4. References for additional reading on subjects associated with airplane upsets and recovery.
Airbus and Boeing encourage all operators to endorse the training recommendations and include airplane upset recovery training in their overall pilot training programs.
Dave Carbaugh
Chief Pilot
Flight Operations Safety
Boeing Commercial Airplane Group
John Cashman
Chief Test Pilot and Director
Flight Crew Operations
Boeing Commercial Airplane Group
Mike Carriker
Senior Engineering Project Pilot -- 737
Flight Crew Operations
Boeing Commercial Airplane Group
Doug Forsythe
Manager
Flight Operations Safety
Boeing Commercial Airplane Group
Tom Melody
Chief Test Pilot and Senior Manager
Flight Operations
Douglas Products Division
Larry Rockliff
Chief Pilot and Director
Flight Training
Airbus Industrie
William Wainwright
Chief Test Pilot
Flight Division
Airbus Industrie

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Copyright © The Boeing Company. All rights reserved.

About IRS's and How They Work

Visit the following link to watch a video about IRS Operation: 
Inertia Reference System (IRS) Operation - B767

About IRS's and How They Work
1. General
A. The inertial reference system (IRS) provides inertial navigation data to user systems. It uses a ring laser gyro instead of the conventional rate gyro to sense angular rate about the roll, pitch and yaw axes. The system is termed strapdown since its sensors are, in effect, directly mounted to the airframe.

B. The inertial reference system (IRS) includes two inertial reference units (IRU), one inertial system display unit (ISDU), one mode select unit (MSU), one master caution unit (MCU), two digital/analog adapters (DAA) and two radio digital distance magnetic indicators (RDDMI). The IRS provides the inertial navigation data and the inertial flight control data to other systems.

C. The main function of each IRU is to sense and compute linear accelerations and angular turning rates about the airplane's pitch, roll, and yaw axes. This data is used for pitch and roll displays and navigational computations.

D. Each IRU contains three laser gyros and three accelerometers. These sense angular rates and linear accelerations, respectively. The sensed data is resolved to local vertical coordinates and combined with air data inputs to compute the following:
(1) position (latitude, longitude)
(2) attitude (pitch, roll, yaw)
(3) true and magnetic heading
(4) windspeed and direction
(5) velocity
(6) accelerations
(7) angular rate data
(8) altitude

E. The IRS outputs are displayed on the flight instrument system displays. They are also displayed on the flight management computer system control display unit (FMCS-CDU) (Ref 34-62-01). Preselected parameters are also displayed on the inertial system display unit (ISDU).

2. IRS Theory of Operation
A. General
(1) The IRS provides basic heading and attitude reference accomplished through computations based on accelerometer and laser gyro sensed signals. Three accelerometers and three laser gyros are used. The accelerometers and laser gyros are of the strap-down type and are positioned in the inertial reference units so that they are oriented along each of the three axis of the airplane. This orientation allows the IRU to sense accelerations along and rotation about each of the three axis. Computer manipulation of the signals from all six sensors provide the basic heading and attitude reference signals along with present position, accelerations, ground speed, drift angle and attitude rate information. The first requirement which must be met for proper IRS operation is alignment. IRS alignment basically consists of determination of local vertical and initial heading.

B. Alignment
(1) IRS alignment consists of determining local vertical and initial heading. Both accelerometer and laser gyro inputs are used for alignment. The alignment computations use the basic premise that the only accelerations during alignment are due to the earth's gravity; the only motion during alignment is due to the earth's rotation. Accelerations due to gravity are always perpendicular to the earth's surface and thus define the local vertical. This local vertical is used to erect the attitude data so that it is accurately referenced to vertical. Initially, only a coarse vertical is established. Once vertical is established, the laser gyro sensed earth rate components are used to establish the heading of the airplane. As the alignment continues, both the vertical reference and the heading determinations are fine tuned for maximum accuracy.

(2) The orientation of the vertical axis of the attitude reference relative to the earth's surface is based on airplane position input to the IRU. The initial position entry can be made at any time during the alignment period. Earth rate sensing by the laser gyros allows the IRU to determine initial latitude. This gyro determined latitude is compared to the crew entered latitude. Crew entered longitude is compared to the last stored longitude. These comparisons must be favorable to complete the alignment period. During the alignment period all outputs of the IRU, except for present position, are set to NCD (No Computed Data). The minimum duration of the align mode is 10 minutes.

C. Navigate Mode
(1) In the navigate mode the IRUs provide outputs for attitude, heading, present position, accelerations, track angle, drift angle, ground speed, and wind data. These outputs are all derived from gyro and accelerometer strap down sensor data. The initial attitude, heading and velocity signals are modified by inputs from the sensors to establish real time present parameters through integration and computer calculations. Additional calculations by the computer establish such parameters as present position, ground speed and drift angle. Inputs from the air data computers are used for inertially smoothed altitude and altitude rate (baro altitude) and wind speed/direction (true airspeed).

D. Accelerometer
(1) Each IRU contains three accelerometers, one for each of the three axes: longitudinal, lateral and vertical. Acceleration along the input axis moves the proof mass. Capacitive pickoff converts the position change into an electrical error signal to the servo amplifier. The servo amplifier nulls out the error signal by returning the proof mass to the zero-position using the torquer coil. The current in the torquer coil needed to null the error signal is the analog output signal representing acceleration.

(2) The analog output signal is integrated once to give velocity and integrated a second time to give distance.

(3) A temperature sensor is provided for each axis (X, Y, Z) to improve accelerometer accuracy. Each sensor provides a signal proportional to temperature. This signal is used by the IRU for compensation and correction of sensor data.


E. Laser gyro
(1) The ring laser gyro uses laser light to measure angular rotation. Each gyro is a triangular-shaped, helium-neon laser that produces two light beams, one traveling in the clockwise direction and one in the counterclockwise direction. Production of the light beams, or lasing, occurs in the gas discharge region by ionizing the low pressure mixture of helium-neon gas with high voltage to produce a glow discharge. Light produced from the lasing is reflected around the triangle by mirrors at each corner of the triangle to produce the clockwise and counterclockwise light beams.

(2) The path length around the cavity is carefully monitored and adjusted so that it is an integral multiple of the peak power laser wavelength.

(3) When the laser gyro is at rest, the frequencies of the two opposite travelling laser beams are equal. When the laser gyro is rotated about an axis perpendicular to the lasing plane, a frequency difference between the two laser beams results. The frequency difference is created because the speed of light is constant. One laser beam will thus have a greater apparent distance to travel than the other laser beam in completing one pass around the cavity.

(4) A small amount of light from the two laser beams passes through one of the mirrors (less than 0.2%). The beams are combined by optical frequencies to produce a beat frequency. This takes the form of a fringe (interference) pattern. This beat frequency of light is analogous to two different audio frequencies which combine to produce a third difference frequency.

(5) When the laser beam frequencies differ, a fringe pattern of alternate dark and light stripes is created. Photodiodes sense the fringe pattern rate and direction of movement. The frequency and relative phase of the two diode outputs indicate magnitude and the direction of the gyro's rotation.

(6) At low rotation rates, the small frequency difference between the laser beams leads to beam coupling. This locks the frequencies together at a single false value. To compensate for this effect a peizoelectric dither motor is used to vibrate the laser block through the lock-in region. Dither vibration has a net zero average. It produces no net inertial rotation. The dither motor vibration can be felt on the IRU case and produces an audible hum.

3. IRS Mode Select Unit (MSU)
A. The mode select unit (MSU) provides mode selection for two IRU's through two mode select switches and monitors the operation of the IRU's through two sets of alert lights mounted on the unit.

B. The MSU is mounted on the aft overhead panel in the flight control cabin. The MSU is mounted with four DZUS fasteners and is interfaced with airplane wiring through two rear mounted connectors.

C. The MSU contains two rotary mode select switches, one for the left (L) IRU and one for the right (R) IRU. The positions are OFF, ALIGN, NAV and ATT.

D. When the mode selector switches are in OFF, power is removed from the IRUs.

E. When ALIGN is selected, power is applied to the IRU's and the IRU's normally progress through an alignment period of approximately 10 minutes before the navigational mode is armed. When the switches are maintained in ALIGN, however, the IRU's remain in the align mode. Normal alignment requires the entry of present position into the IRU's.

(1) The NAV position of the switches enables the navigational mode, provided the alignment period is completed in the IRU's. The NAV position may be selected directly from OFF. The NAV mode is the normal operating mode for the IRS. In this mode, the IRS performs inertial navigation functions and outputs normal IRS data to be displayed or used by other systems.

(2) The ATT position of the switches places the IRU's into a reversionary mode of operation. The ATT (attitude) mode is used when failure or total power loss (AC and DC power) is detected in the NAV mode. In this mode, only attitude and heading data is output to the user systems.

F. Each mode select switch has detented positions. The detented positions prevent accidental movement of the switch. In a detented position, the switch must first be pulled out of the detent before selecting another position to prevent damage to the switch. In the NAV position, the switch must first be pulled out of detent before selecting the ATT position. In the ATT position, the switch must first be pulled out of detent before selecting the NAV position. In the ALIGN position, the switch must first be pulled out of detent before selecting the OFF position.

G. Two sets of four annunciators are installed on the MSU, one set for each IRU. Each set of annunciators consists of an ALIGN annunciator (white when lit) and three warning annunciators (amber when lit). The three warning annunciators are ON DC, DC FAIL, and FAULT. DC power for lamp illumination is derived from the IRU or from the master dim test circuit.

(1) The ALIGN light illuminates steady during alignment or flashes when an abnormal alignment is sensed.

(2) The ON DC lights illuminate when 115 volt ac power is removed from the IRU's and the IRU's operate on 28 volt dc. The 28 volt dc continues to power the left IRU but after 5 minutes, power is removed from the right IRU.

(3) The DC FAIL lights illuminate when the airplane battery power is insufficient to maintain IRU operation.

(4) The FAULT Lights illuminate when an abnormal condition exists in the IRUs.
H. The lights may be tested by pressing each light switch assembly, by activating the bright-dim-test circuit or by initiating an IRU test.

4. Inertial System Display Unit (ISDU)
A.The inertial system display unit (ISDU) provides pilot interface with the IRUs. The ISDU allows entry of initialization data for the IRU's. The display of track angle, ground speed, present position, wind direction and speed, heading and system status is available. The ISDU is located on the aft overhead panel, P5. The unit weighs four pounds (1.8 kgms) and is interfaced with airplane wiring through two rear mounted connectors.

C. The ISDU front panel contains two sets of, seven segmented displays. Mounted on the left side of the front panel is a two-position system display (SYS DSPL) switch and a five position display select (DSPL SEL) switch. On the right side of the panel are a set of twelve keys called the keyboard.

(1) The SYS DSPL switch is a two position switch for selecting either the left or the right IRU. The ISDU can only initialize or receive data from the IRU which has been selected on the SYS DSPL switch.

(2) The DSPL SEL switch selects the type of data to be displayed on the ISDU numeric displays. The IRU, as selected on the SYS DSPL switch, supplies the data. The five switch positions and the data displayed for each position is as follows:

(a) TEST - The test position provides a remote test signal to the selected IRU. When held in the TEST position, fixed outputs from the IRU selected by the SYS DSPL switch are displayed on the ISDU and the associated pilot's instruments. The test switch is inhibited during the navigational mode when the airplane ground speed is greater than twenty knots and during the attitude mode. During the first 2 seconds, all display segments and lighted pushbuttons, except the lightplate lamps, illuminate simultaneously and the highlighter bars on the ENT and CLR keys illuminate. Then, for 8 seconds fault messages are generated which are followed by test value displays.

(b) TK/GS (Track Angle/Ground Speed) - True track angle from 0 to 359.9 degrees is displayed in the left display with a resolution of 0.1 degree. Ground speed from 0 to 2000 knots is displayed in the right display with a resolution of 1 knot.

(c) PPOS (Present Position) - Latitude from 90°S to 90°N is displayed in the left display and longitude from 180°E to 180°W is displayed in the right display. Resolution is 0.1 minute. The display is used when inserting present position during initialization of the two IRUs or when monitoring present position from an IRU during flight.

(d) WIND (Wind speed and Direction) - Wind speed from 0 to 256 knots is displayed in the right display with a resolution of 1 knot. Wind direction from 0 to 359 degrees is displayed in the left display with a resolution of 1 degree. When the airplane is on the ground, the wind speed display will read 100 knots.

(e) HDG/STS (heading/Status) - True heading from 0 to 359.9 degrees is displayed in the left display with a resolution of 0.1 degree. The ALIGN STATUS appears in the left side of the right display and is a countdown of the last 7 minutes of the ALIGN cycle. Malfunction codes (M/C) appear in the right side of the right display.

(3) BRT - A brightness control knob is concentric with the DSPL SEL switch and is a potentiometer to control brightness of the displays.

(4) There are two numeric displays on the ISDU. When the ISDU is receiving IRU data, the DSPL SEL switch determines the data on the display. When the ISDU keyboard is used to initialize an IRU, the data punched in at the keyboard is shown on the two displays. For invalid data from an IRU, both displays are blanked. A brightness control for the displays is located concentric within the DSPL SEL switch.

(5) The keyboard consists of twelve lighted keys. To change the numeric display from the IRU receive mode to a keyboard display mode, one of the following keys must first be pressed, N(2), W(4), H(5), E(6), or S(8). Any other initial key closure is ignored.

(a) N(2), W(4), E(6), or S(8) when pressed the first time cause a N or W to appear in the left display or an E or S to appear in the right display. They represent north, west, east, and south and are used to initialize the IRU when inserting longitude and latitude. Numbered data can now be inserted which will be appropriately displayed on the numeric display (in ALIGN Mode only).

(b) The H(5) key when initially pressed first, also changes the ISDU display to the keyboard display mode. This key is used in the ATT mode to enter the magnetic heading.

(c) Keys with letters on them as well as numbers, represent the letter value when they are the initially pressed key in a program sequence.

(d) When the N, S, E, W or H key is pressed, the ENT highlighter bar illuminates and stays lit while digits are keyed in. When the ENT key is pressed, the ENT highlighter bar extinguishes and a reasonableness check is done on the data. When reasonable, the data is transmitted to the IRU and the display shows the selected parameters.

(e) If the data is unreasonable, the CLR highlighter bar illuminates and the display retains the unreasonable entry. Pressing the CLR key causes the CLR highlighter bar to extinguish and the ISDU to display the selected parameters.

D. The ISDU is powered from both IRU's with 28 volt dc. The two power sources are connected in parallel to the filter which supplies dc for the operation of the unit. A single 28 volt dc source is sufficient to power the unit.

E. Both IRU's supply ARINC 429 format into the ISDU. The system select switch selects one of the busses and supplies it to the processor which continually updates the stored information from the selected bus. In addition, the processor senses pilot inputs during alignment or during the attitude mode. When supplied with information through the keys from the pilot, the processor functions as a transmitter, supplying ARINC 429 information to the IRU's. When the ENT or CLR keys are pressed, the processor functions as a receiver.

F. The processor consists of a clock, synchronized by the selected IRU, a 32 bit register, which converts the ARINC 429 32 bit word to parallel 8 bit information, the data processor which controls unit operation and a bit sensor. The data processor senses discrete inputs from the display selector and controls the display accordingly.

G. The display circuit consists of a display logic, drivers, decoders and 13 display units. The logic circuit senses display selector position, decoder input and dimming control and accordingly controls the light segmented display.

5. Inertial Reference Unit (IRU)
A. The inertial reference unit (IRU) provides attitude, acceleration, angular rates, velocity, true and magnetic headings, positional data, absolute altitude and wind data signals. The signals are developed from a set of three laser gyros and three accelerometers mounted to airplane reference. The signals are provided to other systems including the flight management computer system, the digital flight control system, the electronic flight instruments system, the autothrottle, the VHF navigation system and the pilots' instruments.

B. The IRU has two power sources, one a 115 volt ac source and one a 28 volt dc source. Either source is sufficient for operation but both are required for initial startup.

C. Inside the IRU, the power control circuit automatically switches to a backup source (hot battery bus) when the normal 115 volt ac source is not available. During startup, the control circuit verifies that the battery is connected by switching off the 115 volt ac input. Inputs from the mode select switch controls the power supply switching circuits. The output of the power supply provides control voltage for the IRU and the ISDU and high voltage excitation to the three laser gyros.

D. All IRU input data is routed into the computation circuit. The air data source supplies the ARINC 429 bus input containing air data. Initialization data originates from either the flight management computer or the ISDU. The IRU program pins tell the computation circuits which way the IRU is facing in the airplane.

E. Software does all computations, including compensations, navigational calculations, and coordinate transformations. Gyro and accelerometer outputs are compensated for sensor bias, scale factor, misalignment, and thermal changes. The compensated signals are used in computing airplane pitch, roll and heading relative to the local navigation coordinates. Airplane attitude is used to resolve acceleration into components relative to the local navigation coordinate system. Barometric altitude from an air data computer is used to compensate the vertical speed computations.

F. Three identical ARINC 429 data buses (high speed) provide digital data to flight management, autoflight, and flight instrument systems. A status discrete is applied to the MSU.

G. AIRPLANES WITH IRU -109 AND PREVIOUS;Built-in test equipment (BITE) circuits isolate faults to the LRU level. Faults are indicated by the yellow fault ball on the front of the IRU, the amber FAULT light on the MSU, and a status bit on the data buses to the user systems. The user systems may record an inflight fault based upon the fault from the IRU. In addition, status words are stored in a non-volatile memory in the IRU for at least the previous nine flights. Contents of the non-volatile memory can be extracted on the ground for maintenance.

H. AIRPLANES WITH IRU -110 AND SUBSEQUENT; Built-in test equipment (BITE) circuits isolate faults to the LRU level. Faults are indicated by the amber FAULT light on the MSU, and a status bit on the data buses to the user systems. The user systems may record an inflight fault based upon the fault from the IRU. In addition, status words are stored in a non-volatile memory in the IRU for at least the previous nine flights. Contents of the non-volatile memory can be extracted on the ground for maintenance.

I. Parameters continuously monitored by the BITE include the laser gyros, accelerometer and power supply outputs, computer and memory operation, and temperature. When the IRU is initially turned on, the battery power is tested. The ON DC indication displays during the battery check.
The manual test is initiated by pressing the test switch on the IRU or by holding the display selector in TEST position. The test is also performed as part of the IRS BITE from the FMCS CDU. The test can be done in ALIGN mode, or in NAV mode when ground speed is less than 20 knots. It is inhibited in ATT mode.