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Localizer Performance with Vertical Guidance (LPV)

Instrument Procedures

 


 

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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.]

  • An LPV (Localizer Performance with Vertical guidance) approach is an RNAV (GPS) approach with minimums that are typically lower than LNAV or LNAV/VNAV approaches. An LPV approach is an approach procedure designed specifically for SBAS environments. WAAS/LPV procedures are RNAV approaches defined by the FAA as one of four possible lines of approach minimums found on an RNAV approach chart. WAAS avionics equipment approved for LPV approaches is required for this type of approach.
  • The terms SBAS Approach or SBAS approach operations are used interchangeably with WAAS/LPV approach, or simply, LPV approach. [G-450 OM 2B-08-120, Section 27.B]

More about: G450 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.]

  • SBAS is a wide area coverage augmentation system. The user receives GPS constellation augmentation information from a geostationary satellite-based transmitter. SBAS complements the core GPS satellite constellation by increasing navigation accuracy, integrity, continuity and availability provided within a service area. The U.S. SBAS is WAAS.
  • The Space-Based Augmentation System (SBAS) is the implementation of a ground sensor-generated correction signal transmitted to an SBAS-equipped GPS receiver by way of a geosynchronous satellite. Several countries and/or groups of countries are developing their own SBAS system with their own respective names. The SBAS systems in development at this time are as follows:
    • Wide Area Augmentation Systems (WAAS) for the United States and Canada
    • European Geostationary Navigation Overlay System (EGNOS) for Europe
    • Multifunction transportation Satellite-based Augmentation System (MSAS) for Japan

[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

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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: 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.

[AC 90-107 ¶10.c.] Parts 91K, 121, 125, 133, 135 and 137 operators receive approval to fly RNAV (GPS) instrument approaches via OpSpec/MSpec/LOA, paragraph C052, OpSpec/MSpec paragraph H102 or OpSpec/MSpec paragraph H122, Special Non CFR Part 97 Instrument Approach or Departure Procedures for Rotorcraft Operations, as applicable. If the operator has already been approved to fly IAP with vertical guidance using RNAV (GPS) or RNAV (GNSS), such as baro-VNAV, then no further authorization is required. If the operator is not already approved to fly IAP with vertical guidance using RNAV (GPS) or RNAV (GNSS), the Principal Operations Inspector will authorize LPV and/or LP operations for the operator via OpSpec/MSpec/LOA, paragraph C052, OpSpec/MSpec paragraph H102 or OpSpec/MSpec paragraph H122.

Operational Approval - International (Commercial)

International approval really depends on the host nation and there isn't a clean answer, especially for commercial operators. The first question you have to ask is which LPV approaches are eligible? The standard C052 template doesn't address this and chances are your C052 is quiet on the subject. You can, optionally, have another template used but even that is only good for GNSS-based appraoches. Remember that your C052 must specifically list this approach type for you to shoot it.

[FAA Order 8900, Vol 3, Ch. 18, Part C, C052] An optional LOA template is provided to satisfy a request from foreign regulatory authorities for evidence of training and approval to fly GNSS-based approaches. Unlike the other C052 templates, the inspector only has the option of GLS or RNAV (GNSS) approaches to LNAV, LNAV/VNAV, LPV or Localizer Performance (LP) lines of minima. As a result, this LOA is not a comprehensive list of authorized approaches for the operator, but only a subset to address foreign GNSS-based approaches.

Operational Approach - International (General Aviation)

In the United States, Part 91 operators don't need an LOA so long as they meet the requirements in AC 90-107 ¶10.a., shown above. But that advisory circular specifically says it only applies to operations in the United States. Here are again you are required to ensure you meet host nation rules. In late 2015 it became evident some countries did indeed require an LOA and FAA Notice 8900.318 supposedly lays out the process. I've heard FSDO's are very reluctant to do this.

So that leaves open the question: can you fly an LPV approach internationally? The more important question is this: can you fly a RNAV(GNSS) approach internationally? The basic answer is that ICAO Doc 8168 Vol 1 says you can if your aircraft is qualfied, you have the necessary knowledge, the country has approaches based on a compatible navigation system, you have an alternate, and the procedure is in your database. Left unsaid is that any nation can take exemptions to these procedures and require more from you. More about this: RNAV(GNSS) Example. So if you meet all the qualifications in the United States, you need to make sure the country you are visiting doesn't have any extra prohibitions are stipulations. The best way to do that is comb your Jeppesen ATC pages.

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.

  • ICAO recommendations suggest that regulatory agencies require operational approvals for Performance Based Navigation (PBN)-type procedures (RNAV, RNP, LPV, etc.). EASA is following the recommendations for both commercial (US Part 121/135 equivalent) and non-commercial (US part 91 equivalent) operators of European-registered aircraft.
  • The FAA, however, filed a deviation from the ICAO requirements and does not require a formal approval (LOA) for all PBN procedures. As a result, Part 91 operators aren't required to possess an LOA for LPV approaches.

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"]

  • Honeywell Flight Technical Services has received several questions regarding the use of an LPV approach as a backup to a visual approach. Many pilots are familiar with using a localizer and glideslope as a backup when flying a visual approach, but does loading an LPV approach work just as well?
  • Having course guidance and a vertical path helps to maintain a stabilized approach. However, using an LPV to backup a visual approach does have its limitations. For example, if a turn onto final occurs inside the FAF, or a side step to another runway is required, the excessive deviation monitor may remove information from the display.
  • Pilots are aware that the ILS transmitter is located physically on the field and projects a signal that is then directly received by the aircraft. With an LPV approach, the FMS navigation database contains the final approach segment (FAS) data block associated with the LPV minimums for the RNAV procedure. The FAS data block consists of the lateral and vertical definition for the final approach path to be flown during the approach. The FAS data block is transmitted from the FMS to the Global Navigation System Sensor Unit (GNSSU) and is used to compute the aircraft lateral and vertical deviations for the final approach segment.
  • As mentioned previously, there is a monitoring system in the GNSSU for excessive deviations. This monitor is set to trip when either lateral or vertical deviation exceeds two dots of deviation when inside the FAF. The system supplies the pilot with an annunciator in the event of an excessive deviation from the defined LPV final approach segment. This annunciator may be displayed as a flashing lateral or vertical deviation scale in aircraft equipped with an integrated LPV PFD solution, or for aircraft with an external annunciator, an LPV UNAVAIL annunciator is lit and the lateral and vertical deviations are flagged invalid. The annunciator for excessive deviation occurs when the aircraft position has exceeded a set deviation limit (one or two dots of lateral or vertical deviation, depending on the aircraft) while the aircraft is inbound to the runway. The excessive deviation detection initiates 2 NM prior to the FAF and is active until reaching the MAP.
  • If an RNAV approach with LPV minimums is selected as a backup to a visual approach, be familiar with the excessive deviation logic found in the AFM. If expected to fly direct to, turn final inside the FAF, or possibly side step and exceed two dots lateral deviation, it is recommended that LNAV or LNAV/VNAV minimums is selected from the approach page on the CDU. This will eliminate the possibility of a loss of any advisory information.

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

FAA Order 8900, Vol 3, Ch. 18, Part C, C052, 10/26/15

FAA National Policy N 8900.318, Optional LOA for Straight-in Non-Precision, APV, and Category I Precision Approach and Landing Minima - All Airports, 8/13/15

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"

Revision: 20160427
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