What are LNAV/VNAV, LPV and LP approaches?

What are LNAV/VNAV, LPV and LP approaches?

LNAV is a non-precision approach. It uses GPS and/or WAAS for lateral navigation, but there’s no vertical guidance. Typically it takes you down to 400 ft.

LNAV/VNAV again is a non-precision approach. It provides lateral guidance from the GPS or WAAS receiver and vertical guidance from a barometric altimeter or the WAAS. Without WAAS, you must have a VNAV altimeter. Decision altitude is typically around 350 ft.

LPV? LPV is a non-precision approach. It stands for Localizer Performance with Vertical Guidance and uses the WAAS GPS only. It is the most desired approach that you can be offered. It typically takes you down to 200-250 ft decision height.

LP. It is a future approach that will use the high precision of LPV for lateral guidance, and a barometric altimeter for vertical. Runways where obstacles or infrastructure limits are, vertically guided approaches cannot be published.

LPV Operational Benefits

Currently over 1,975 runways across the United States and more to come. Many approaches have minimums to 200 ft height above touchdown and ½ mile visibility with greater accuracy and consistency.

Once you’ve flown a GPS approach with LPV you’ll be amazed at how the aircraft performs and how stable it is. Electronic glide paths eliminate intermediate step down approaches, or dive and drive approaches. This type of approach provides more comfort for your passengers, less ear popping, and just more comfort and safety overall. The glide path become independent of ground or barometric equipment. Everything is calculated internal to the aircraft.

WAAS and LPV eliminate:

• cold temperature effects,
• incorrect altimeter settings,
• and lack of local altimeter source

If I install WAAS-capable equipment, am I ready to fly LPV approaches?

Questions that we’re often asked are if I install WAAS-capable equipment, am I ready to fly LPV approaches? The answer is no. WAAS receivers cannot be installed under a straight field approval. There’s a lot more to the field approval process. Once it’s installed in the aircraft, the installing agency needs to make sure that all equipment in the airplane is properly functioning. That means the autopilot, the scaling, everything that becomes a part of this equation needs to be checked, so it’s a lot more stringent than a straight field approval. Most WAAS receivers are installed under an STC.

WAAS-capable avionics do not automatically mean that you can fly to an LPV minimum. To accomplish the LPV minimums, you need dual WAAS receivers. They must be certified under TSO 145/146.

Can I upgrade my existing navigational system to a WAAS receiver?

We’re often asked the question can I upgrade my existing navigational system to a WAAS receiver and the answer is no. Current systems are certified under TSO C129, a completely different criteria. TSO C145 and 146 means that the units are certified as a standalone receiver. No other signal needs to go into that box in order to give it the accuracy that it will present on your aircraft instruments.

It also requires an antenna change. The antenna’s are different from the TSO 129 box to what’s certified on a 145/146. Installation is currently being done by STC and requires:

• dual GPS receivers,
• other equipment mods, such as the scaling and autopilot,
• annunciation, whether it’s external or on an EFIS system,
• and a flight test procedure are all required.

Airports with WAAS approaches

This map shows some of the airports (see presentation slides) that are across the United States.

The WAAS/LPV Approach Plate

The LPV approach on an approach plate is called out (see presentation slides). You’ll see that it says “WAAS Approach” on it. So just like any other approach, GPS approach, VOR approach, ILS… it calls out particular criteria. So you take the approach appropriate to that airport, channel it up in your receiver and fly the approach.

Contact Gary Harpster or a member of Duncan Aviation's Avionics Installation Sales team for more information.

Understanding WAAS/LPV Video Series

	WAAS Considerations: Introduction July 1, 2010 - Gary introduces the video series with a brief overview of key topics to consider if your aircraft isn't equipped with WAAS, including legacy interface problems, field approvals, annunciators, Next-Gen criteria, and how to determine if your aircraft is a candidate for an upgrade. » Watch "WAAS Considerations"
	Part 1: What is WAAS? July 8, 2010 - Find out how WAAS is a part of the FAA's Next-Gen initiative, the system network and coverage, and why installing WAAS-capable equipment doesn't mean you're ready to fly LPV approaches.. » Watch "What is WAAS?"
	Part 2: How WAAS Works July 15, 2010 - Learn how WAAS interacts with GPS signals, what augmentation messages do, and how they're processed. » Watch "How WAAS Works"
	Part 3: WAAS Benefits July 22, 2010 - Learn how WAAS changes navigational system accuracy, approaches, flexibility, precision, fuel savings and government and airport costs. Operational benefits and Next-Gen considerations are also discussed. » Watch "WAAS Benefits"
	Part 4: What is LPV? July 29, 2010 - Learn what LPV approaches are, how they benefit operators, and common equipment questions. » Watch "What is LPV?"