Existing primary flight instrumentation "is no longer adequate and safe for the developing RNP (required navigation performance) environment", says the International Federation of Air Line Pilots Associations (IFALPA).
RNP approaches are increasingly widely used in many countries for airports located in complex terrain, and may soon become the preferred system for non-precision approaches. In the long term, it is likely to replace existing precision approach aids, such as the instrument landing system.
RNP approaches, increasingly used for awkward approaches in challenging terrain, are flown using a global navigation satellite system (GNSS)-based guidance system, with accuracy specified according to the on-board equipment capability and the type of GNSS augmentation in the area, if any.
IFALPA has proposed a primary flight display (PFD) design that contains all the information required to enable pilots to fly RNP approaches accurately, and to recognise deviation from the ideal trajectory immediately (see diagrams).
It explains: "The Federation says there is an immediate need to update the capabilities of the avionics displays in order that they become equal to the task."
Referring to the latest "glass cockpit" displays, IFALPA says: "Progress has been made with the development of the modern navigation display (ND) compared with the earlier design horizontal situation indicator for use in VOR navigation and ILS approaches. However, the depiction scale used on the present ND will not provide the resolution required by the RNP environment."
That is not all, says IFALPA, pointing out that information and guidance for pilots during RNP approaches is scattered across two neighbouring displays, and some data has to be called up by the pilots because it is not on the main screens.
"At present," says the Association, "the only actual guidance given to the crew is flight guidance information delivered via the FD.
Furthermore, the information needed to monitor the system performance of the aircraft for the procedure flown is widely scattered throughout the cockpit. For example, the lateral deviation is only displayed on the ND as a numerical value [such as 0.2L].
"In some systems, the information relating to availability for Navaids like GPS receivers and satellites are buried in the third layer of pages on the flight management computer or the multi-function control and display unit."
IFALPA warns: "Position information or, better still, situation information is not available via the PFD. This, in turn, leads to the crew having degraded situational awareness.
"This can result in the crew being limited to a reactive response to deviations by the flight guidance and control system rather than having the ability to look ahead and anticipate deviations and the required corrective actions."