Definition for "New advanced aircraft"

[Robert Woodhouse]

Advice request – a definition of “Advanced aircraft”

I am working with a group involved in the development of criteria for instrument procedures. A number of agencies have been asking for the design criteria to be updated to reflect the capabilities of modern “Advanced aircraft”. Unfortunately they have not yet produced a workable definition of this new class of aircraft – a definition that has to translate to yet another set of minima on an instrument approach chart.

This class of aircraft might benefit from smaller lateral and vertical approach volumes for precision approaches, and in reduced height loss values (due to modern piezoelectric altimeter sensors).

So far three possible definitions have been identified:

1) RVSM approved aircraft – these aircraft must have modern altimeter systems better than the direct drive models assumed in current ICAO criteria. Unfortunately the altimeter specification is geared to performance above 29000 ft and is not expressed in a way that is easily translated into mean and standard deviation values at normal instrument procedure altitudes.

2) RNP approved aircraft – unfortunately the standard RNP criteria deals only with lateral performance and even 0.1 RNP is large compared with current precision approach criteria. The upcoming RNP/AR (ICAO version of the FAA-SAAAR criteria) does contain a more stringent altimeter error requirement. However, the rather extensive aircraft and operational approval requirements mean that the number of approved operators is likely to be small.

3) Aircraft first certificated after 1982. Various sources have suggested that all such aircraft would have improved altimeter systems (at least for Part 121 aircraft).

If anyone has comments or alternative suggestions, now is the time such advice would be very useful.

Many thanks
Robert

[ICT_SLB]

Robert,
It sounds like your group is effectively re-inventing the FAA AC 90-101 - SAAAR. If you read between the lines you'll find FMS with WAAS or better GPS requirements (14m lateral if memory serves), IRS for the brief times GPS does have an off-day ("coasting"), Autopilot capable of an MEH of less than 400 feet agl - not easy to obtain IMHO, CPDLC etc. Overall it becomes a shopping list of what consitutes an "Advanced Aircraft" at least from the AP, NAV & COMMS perspective.

A question of my own - if the Lateral NAV is so near perfect - how do you verify its performance? Or will it be like GPS when it came out - it's correct don't question it.

This whole subject is probably closer to Flight Testing at least from the Certification point of view, maybe it should be posted on that forum?

[bflyer]

Hi eveybody
IMHO as an operator, it will come down to better autopilots and better radio altimeters

[ICT_SLB]

Bflyer,
Sorry, can't agree. Rad Alts are already down to 2 ft accuracy & you have been able to install zero/zero Autopilots for about 40 years (Trident or L1011). The big new requirement is to shave the lateral clearances between both obstructions so, for arguement sakes, you can fly around the hillside and then turn onto runway centerline at SFO, and aircraft on parallel runways (SFO again). As I said, look at AC 90-101, the approach diagrams will probably give you sleepless nights as it shows clearances not much more than wingspan.

[bflyer]

Hi ICT
So if the autopilots and radio altimeters are at a developement dead end so to speak and IMHO you cannot reduce tolerences unless you come up with better equipment..what else is there?
I already have sleepless nights thinking about some of the approaches out there
Question is can the available airspace be squeezed more?..i think not

[Robert Woodhouse]

I fear my request was not sufficiently clear, since I fear we are getting off track a little.

First, thank you ICT SCF, you are of course correct that SAAAR approved aircraft are one easily identified group, and the new ICAO PBN Manual does contain a manufacturer agreed altimeter error specification. However, I was invoved with the ICAO adaptation of that criteria and know that not many operators are likely to go the expense of the related approval processes. Thus SAAAR approved aircraft are certainly an appropriate group, but they are a small sub-group of the "modern advanced aircraft" group we need to identify.

Second, I should have made it clearer that we are looking for a category that excludes the older or non-FMS aircraft and is restricted to aircraft with modern avionics and modern piezoelectric altimeter systems.

Be aware that the PANS-OPS height loss values used to determine precision approach OCA/H are based on direct drive altimeters (the source was the 1967 Report of the UK Board of Trade All Weather Operations Committee). This report gave a mean bias error of 9m. Since Honeywell tell me that piezo elecrric altimeters have no hysteresis (bias) then this class of aircraft could gain an immediate operatinal benefit of 9m - not a huge amount but a start.

While this seems a simple solution, my basic question remains - how do we identify this class of aircraft? As I said in my first post, RVSM approval might imply the use of a modern altimeter, but unfortunately the equipment specification does not address performance in the approach phase. However, it remains a possibility. The other possibility was aircraft first approved after 1982.

RE the comment about radio altimeters - this change is directed to ILS/MLS and GBAS for Category I operations, where the pressure altimeter applies.

Thank you for the suggestion that this topic might best be moved to the flight test forum - and I leave that to the administrator.

Many thanks for all input
Robert

[ICT_SLB]

If you're going to just predicate this on the type of altimetry used, then "aircraft with dual air data computers" might just fit and be relatively easy to differentiate. Remembering all the agonizing that occurred with RVSM ADCs (including altitude drift with time caused by the piezo-electric sensors) this might be too simplistic if overall accuracy is what you're really try to confirm.