Performance Based Navigation (PBN) is a significant enabler of efficiency and safety in Business Aviation. Mario Pierobon speaks with Universal Avionics’ Carey Miller to discuss the advantages and requirements for a Flight Department to benefit…
Traditionally, air navigation relied on ground-based infrastructure. With the advent of Global Navigation Satellite Systems (GNSS) and the ever-increasing accuracy GNSSs are able to guarantee when their signals are augmented by a Satellite-Based Augmentation System (SBAS), ground stations are being progressively decommissioned and PBN is opening up navigation opportunities without the need for ground infrastructure.
PBN operations are based on performance requirements expressed in navigation specifications – area navigation (RNAV) and Required Navigation Performance (RNP) – in terms of accuracy, integrity, continuity, availability and functionality needed for the proposed operation.
RNAV and RNP navigation specifications are very similar – the only difference is that RNP has a requirement for on-board performance monitoring which RNAV does not have.
Under the RNP family of navigation specifications there is the RNP approach to localiser performance with vertical guidance (LPV) minima [RNP APCH (LPV)] which is becoming particularly popular in Business Aviation because it makes it possible to conduct an Instrument Landing System-like approach without actually needing an ILS, and with decision altitudes down to 200ft.
The ability for a corporate flight department to conduct LPV approaches does not come automatically. There are distinctive requirements to satisfy (in terms of operating procedures to develop), training to undertake and equipment to qualify.
However, unlike other PBN navigation specifications (i.e., the RNP authorization required (AR) APCH) LPV approach operations are not subject to a specific approval.
A corporate flight department must amend the operations manual to support LPV approach operations and procedures must be developed for both normal and abnormal operations.
Regarding normal operations, specific procedures must be developed for pre-flight planning, prior to commencing the procedure and during the procedure.
Abnormal procedures must address cautions and warnings resulting from conditions, such as the failure of the navigation system components. This would include those affecting flight technical errors, such as:
- Failures of the autopilot
- The loss of integrity annunciation
- The warning flag or equivalent indicator on the lateral and/or vertical navigation display and
- Degradation of the GNSS approach mode during an LPV approach procedure (i.e. a downgrade from LPV to LNAV).
“Given the LPV approach is another type of approach with both vertical and lateral guidance similar to an ILS, no specific risks are associated with an LPV approach,” Carey Miller, Director of Business Development at Universal Avionics told AvBuyer. “However, the aircraft Flight Management System (FMS) for the installed equipment that allows the airplane to fly an LPV must list the LPV approach as an approved approach type.
“As opposed to a traditional ILS approach, an LPV approach implies that the specific approach be loaded into the FMS, instead of the old-style navigation controller. When it is loaded into the FMS the missed approach guidance is loaded as well.”
Flight Crew Training
As part of setting up the LPV capability within a Flight Department, the flight crew training program must be structured to provide sufficient theoretical and practical training in the concept of RNP approach operations to LPV minima, and the use of the aircraft’s approach system in such operations to ensure that flight crew are not just task-oriented.
The minimum flight crew training syllabus should cover RNP approach concepts and operations containing LPV minima. “Every flight crew should understand how to use the FMS to the point of loading LPV approaches,” Miller emphasized.
“Essentially, if you are an operator you should know how to use the FMS, as the LPV approach is another approach selection that you need to know how to input.
“We typically have an approach section or an approach page where there are different approach options, one of them being an LPV approach. Once selected and integrated it is ready to be flown. It depends on the level of integration of the FMS, but overall it is just like a traditional ILS approach.”
Developing Critical Mass
LPV approaches are developing critical mass as business airports increasingly publish LPV procedures. The relevant procedure must be developed by a flight procedure design organization and it must be published in the Aeronautical Information Publication (AIP).
Developing a procedure like an LPV approach must be done professionally and in a controlled way, but it remains much less expensive than setting up an ILS.
“In the US there is nothing holding the FAA back from publishing these approaches. Of course, they must be thoroughly designed and physically flown to make sure that everything is Ok, but the benefits are self-explanatory when an LPV costs in the range US$50k to develop and publish as opposed to $1m to set up an ILS.
“The fact that they are much cheaper to develop and implement is why there are more and more being published. As of June 2018, there were 3,909 Wide Area Augmentation System (WAAS) LPV approach procedures serving 1,900 airports – 1,138 of these airports are non-ILS airports.
“Currently, there are also 661 Localizer Performance (LP) approach procedures in the US serving 495 airports. Given the number of non-ILS airports that LPVs serve, this effectively opens up an additional 1,138 airports to ILS-like approach capability,” Miller continued. “This does not count the number of additional airports made available through compatible systems in Europe through EGNOS.”
Meeting the ADS-B Out Mandate
One of the requirements for the ADS-B Out mandates in the US and Europe is an SBAS (or WAAS) FMS to provide improved position accuracy. “When you have equipped for LPV, you are half-way to meeting the ADS-B Out mandate already,” Miller noted.
ADS-B Out requirements in the US and Europe essentially require that more information be given by the aircraft to the controller, and that this be done in a faster way.
“Part of the solution for ADS-B Out is not only updating the transponders but also updating the GNSS navigation source. What is required is a WAAS (SBAS) GPS that’s more accurate. If an operator equips for LPV the only additional items they will have to update are the transponders for the ADS-B Out mandate.”
Reporting Safety Events
LPV approach operations are required to be integrated into the Flight Department’s Safety Management System (SMS), especially regarding events that adversely affect the safety of the operation and may be caused by actions or events external to the operation of the aircraft navigation system.
A Flight Department should have a system for determining whether such events are due to an improperly coded procedure, or a navigation database error. The responsibility for initiating corrective action resides with the operator.
Depending on the regulatory requirements, technical defects and the exceeding of technical limitations may be the subject of occurrence reports. These instances include significant navigation errors attributed to incorrect data or a database coding error, unexpected deviations in lateral or vertical flight path not caused by pilot input or the erroneous operation of equipment as well as significant misleading information without a failure warning.
Other reportable occurrences are the total loss or multiple navigation equipment failure and the loss of integrity annunciation where SBAS for LPV approach operations had not been notified as unavailable or unreliable during pre-flight planning.