Eddie Sez:

An LPV approach is rapidly becoming the way to go just about everywhere you go. It gives you the accuracy of an ILS without the problems of localizer or glide slope interference. The chief advantages are in two directions:

  • Laterally you are almost guaranteed to end up with the runway numbers in front of you, much better than a standard RNAV approach. On most aircraft, the azimuth on an LPV approach decreases as you get closer, just like an ILS. That isn't true with an RNAV approach.

  • Vertically you also get the decreasing azimuth, just like an ILS. But you also get a vertical navigation that doesn't need to be temperature compensated, as is true with an LNAV/VNAV approach.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.


Figure: Example RNAV (GPS) Approach LPV Line of Minima, from AC 90-107 Appendix 2, page 1.


General Description

[G450 Aircraft Operating Manual §2B-08-120 ¶27.B.]

More about: G450 Procedures & Techniques / LPV Approach.

WAAS Overview

[AC 90-107 ¶6.b.] WAAS improves the accuracy, integrity, availability and continuity of GPS signals. Additionally, the WAAS geostationary satellites provide ranging sources to supplement the GPS signals. If there are no airworthiness limitations on other installed navigation equipment, WAAS avionics enable aircraft navigation during all phases of flight from takeoff through vertically guided approaches and guided missed approaches. WAAS avionics with an appropriate airworthiness approval can enable aircraft to fly to the LPV, LP, LNAV/VNAV and LNAV lines of minima on RNAV (GPS) approaches. One of the major improvements WAAS provides is the ability to generate glide path guidance independent of ground equipment. Temperature and pressure extremes do not affect WAAS vertical guidance unlike when baro-VNAV is used to fly to LNAV/VNAV line of minima. However, like most other navigation services, the WAAS network has service volume limits, and some airports on the fringe of WAAS coverage may experience reduced availability of WAAS vertical guidance. When a pilot selects an approach procedure, WAAS avionics display the best level of service supported by the combination of the WAAS signal-in-space, the aircraft avionics, and the selected RNAV (GPS) instrument approach.

Satellite-Based Augmentation System (SBAS)

[AC 90-107 ¶4.u.]

[G450 Aircraft Operating Manual §2B-08-120 ¶27.A.] Although several SBAS systems are currently under development, they are all expected to be compatible and interoperable.

Approved Vertical Guidance

[AC 90-107 ¶4.b.] Actual vertical path deviation guidance indications generated by certified means for charted approach procedures that contain a U.S. Standard for Terminal Instrument Procedures (TERPS)-protected glide path (e.g., approaches with LNAV/VNAV, LPV or ILS lines of minima).

Decision Altitude (DA)

[AC 90-107 ¶4.g.] In an approach with approved vertical guidance, DA is a specified altitude expressed in feet above mean sea level (MSL) at which a missed approach must be initiated if the required visual references to continue the approach have not been established.

Localizer Performance with Vertical Guidance (LPV)

[AC 90-107 ¶4.o.] An RNAV function requiring WAAS, using a final approach segment (FAS) data block, which computes, displays and provides both horizontal and approved vertical approach navigation to minimums as low as 200 foot ceiling and ½ mile visibility.

LPV Lines of Minima

[AC 90-107 ¶6.e.] RNAV (GPS) approaches to LPV lines of minima take advantage of the improved accuracy of WAAS lateral and vertical guidance to provide an approach that is very similar to a Category I (CAT I) ILS. Just as with an ILS, LPV has vertical guidance and is flown to a DA. The design of the LPV approach incorporates angular guidance with increasing sensitivity as an aircraft gets closer to the runway (or point in space (PinS) type approaches for helicopters). The sensitivities are nearly identical to those of the ILS at similar distances. This was done intentionally to allow the skills required to proficiently fly an ILS to readily transfer to flying RNAV (GPS) approaches to the LPV line of minima.


European LPV

Figure: Le Bourget EGNOS Approach Example, from Jeppesen Airway Manual, LFPB Page 32-3, 31 Jan 14.

The European version of WAAS is EGNOS, European Geostationary Navigation Overlay System. The ICAO Document covering this is still in draft. Can you fly this? I think so. The process for making this determination is here: Procedures & Techniques / RNAV (GNSS) Example. In the case of this approach, France is WGS-84 compliant but the Jeppesen Airway Manual ATC Pages for France are bit obtuse about this. The 24 Jan 2014 version says: "The GNSS approach clearance is requested by the pilot after checking that it could be undertaken." Given that, I think I would prefer the ILS but it seems this approach would be acceptable.

EASA is recommending its members require operational approval before allowing aircraft to conduct LPV approaches. While none, as of April 2014, have codified such a requirement, you should arm yourself. See Operational Approval - EU, below.


Equipment Requirements

You will have to consult your aircraft manuals, for a G450:

[G450 Airplane Flight Manual §1-03-10 ¶10.E.] RNAV-SBAS: ASC 059B (or later approved revision) required to fly an RNAV (GPS) or an RNAV (GNSS) approach to LPV minima.


Regulatory Requirements

Advisory Circular 90-107, Guidance for Localizer Performance with Vertical Guidance and Localizer Performance without Vertical Guidance Approach Operations in the U.S. National Airspace System, 2/11/11, U.S. Department of Transportation


Operational Approval - U.S.

[AC 90-107 ¶10.a.] Part 91 Operator/Aircraft Approval. Part 91 operators should review their AFM, RFM or AFMS to establish that their aircraft meets navigation system eligibility as detailed in paragraph 7. Once the operator has established system eligibility, the operator should review the operational and training considerations as detailed in paragraphs 8 and 9. After completing these actions, the operator may conduct LPV and LP approach operations to a published DA and MDA, respectively. An LOA is not required when eligibility is based on the AFM, RFM or AFMS and provisions of this AC.


Operational Approval - EU

The European Aviation Safety Agency (EASA) issued guidance to European state aviation authorities requiring approvals for general aviation operators under European jurisdiction. There is not, as of April 2014, any all-encompassing requirement or method to answer the requirement.

Is that good enough? Well I guess if you aren't European-registered you should be good to go. But you should still consider carrying documentation on board to show aircraft and flight crew compliance with LPV requirements, such as:


Advantages

An LPV approach uses WAAS (which is the US version of SBAS) to provide a space-based precision approach that flies like an ILS both laterally and vertically, but isn't subject to ground interference. The glide path narrows like an ILS but isn't affected by temperature like an LNAV/VNAV.


Disadvantages

Can you use an LPV approach to back up a visual joined inside the FAF? No, not really:

[Honeywell Direct To Newsletter, Nov 2013, "LPV Approach as a Visual Approach Backup"]


References

Advisory Circular 90-107, Guidance for Localizer Performance with Vertical Guidance and Localizer Performance without Vertical Guidance Approach Operations in the U.S. National Airspace System, 2/11/11, U.S. Department of Transportation

Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

Honeywell Direct To Newsletter, Nov 2013, "LPV Approach as a Visual Approach Backup"