Can the FPV be used to determine AOA

[JammedStab]

In smooth air or turbulent air?

[Dan Winterland]

If you combine the FPV and attitude, then technically yes. However, you will also need to know what reference the attitude is taken from (one would assume the body angle) and compare this with the angel of incidence. So it's a bit complex.

Several accident reports have mentioned that an angle of attack indication would have been useful to the unfortunate crew and I gather it is an option on the A320 family. But no customer seems to fit it. I have flown aircraft with AoA gauges (all military) and they are very useful.

[wiggy]

I'd be very careful, especially if you are dealing with a "non-normal" and above all check what your type's FCOM has to say on the subject.

Certainly on some Boeings there's an Air Data input to the FPV. As a result there is a warning in the 777 QRH that for at least one Flight Instrument non-normal that you must not use the FPV.

[FE Hoppy]

On the Ejets not only can it be used but it is the primary indication of alpha margin in conjunction with the PLI.

The non-normal caveat already stated also applies.

[tom775257]

To quote forum member OPEN DES directly from another thread regarding the A320:

"FPV is actually a derivative of Vzbi. Vzbi is baro-inertial vertical speed, i.e.: the one we see indicated in normal conditions.
FPA is derived using GS and Vzbi.
In conditions where Vzbi is not available FPA is derived from the difference between pitch and AoA, this is however a degraded FPA, relative to the air only"

[Volume]

It is not so much a question of smooth or turbulent air, it is a matter of the (constant) motion of the surrounding air. In a windshear situation (in a downburst) when you need it most it will have the greatest error. In calm air you do not need it.
Given the fact that any large transport aircraft does have an AoA sensor, it is just a matter of installing the indicator (or to implement the indication into your PFD). So what do you win if you calculate AoA from other data? The AoA data is there.

[JammedStab]

In a windshear situation (in a downburst) when you need it most it will have the greatest error. In calm air you do not need it.


So I have it in calm air?

[de facto]

In no wind yes...your angle of attack is the difference between your pitch (angle of incidence) and FPV angle.

[Denti]

In no wind, with no air data malfunction, not climbing nor descending. Easier to ask your airline to pay for the AoA indication. It is available as customer option after all.

[de facto]

From an airbus/boeing doc discussing about loss of control,upset recovery...

The flight path angle is the angle between the flight path vector and the horizon. This is also the climb (or descent angle). On the newest generation jet transports, this angle can be displayed on the primary flight display (PFD), as depicted in Figure 18. Flight path angle can also be inferred from the vertical speed indicator (VSI) or altimeter, if the ground speed is known. Many standard instrument departures require knowledge of flight path angle in order to ensure obstacle clearance.
Angle of attack is also the difference between the pitch attitude and the flight path angle with no vertical wind component. The angle of attack determines whether the aerodynamic surfaces on the airplane are stalled or not.

[FLEXPWR]

On A320 (and probably on other Airbus types too) the AoA value is available in Alpha Call up MCDU maintenance pages. However it displays only the values for ADR's AoA #1 and #2 if I recall, the SBY (#3) can't be shown.

I remember some A320 in Air Inter (absorbed by AF in the late 80's or early 90's) had an AoA "analog" gauge displayed just below the PFD/ND control panel, but only on the captain's side.

[Winnerhofer]

I've never seen any Boeing with an AOA display.

[Kefuddle]

If you combine the FPV and attitude, then technically yes. However, you will also need to know what reference the attitude is taken from (one would assume the body angle) and compare this with the angel of incidence. So it's a bit complex.
Have I glossed over something? I reckon the simple difference between the FPV and PFD attitude in all phases is the angle of attack (within the limitation of the FPV capabilities of course).

[Check Airman]

I've never seen any Boeing with an AOA display. It's the circular gauge at the top right corner of the PFD.

Photos: Boeing 737-823 Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/American-Airlines/Boeing-737-823/1607802/M/&sid=71bc1affb589fbef0a000f19113d3570)

Photos: Boeing 777-223/ER Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/American-Airlines/Boeing-777-223-ER/2370692/M/&sid=71bc1affb589fbef0a000f19113d3570)

[Check Airman]

Here's a good write-up from Boeing on their AoA gauge.

Aero 12 - Angle of Attack (http://www.boeing.com/commercial/aeromagazine/aero_12/attack_story.html)

It includes a nice diagram.

http://www.boeing.com/commercial/aeromagazine/aero_12/images/attack_fig13.jpg

http://www.boeing.com/commercial/aeromagazine/aero_12/images/attack_fig13.jpg

I couldn't find any information on an Airbus AoA gauge.

[JammedStab]

So in smooth air with no malfunctions, is it

In no wind, with no air data malfunction, not climbing nor descending.

level flight only or

Have I glossed over something? I reckon the simple difference between the FPV and PFD attitude in all phases is the angle of attack (within the limitation of the FPV capabilities of course).

all phases of flight.

[Winnerhofer]

AOA Indicator:Make It Standard! — Tech Ops Forum | Airliners.net (http://www.airliners.net/aviation-forums/tech_ops/read.main/304948/)

[Chris Scott]

The difference between Pitch and FPA certainly gives a rough guide to AoA, particularly changes of AoA. As has been said by others, it should be correct in still air, but becomes increasingly inaccurate as the headwind or tailwind component increases. That's because FPA is in relation to the earth, not the airmass. (So vertical movement of the airmass, particularly a microburst, will also cause inaccuracy.)

The wind-component problem is perhaps best illustrated by considering the extreme case where headwind equals TAS, in which case any rate of climb or descent would produce (unreadable) FPAs of +90 and -90 respectively.

[Denti]

As posted above the FPV in boeing and airbus is not completely inertial, it receives air data input as well. Boeing used to promote its use in some non normal scenarios but have since removed those remarks or put some in that warn pilots not to use the FPV.

For AoA indication boeing offers an AoA gauge on the PFD as customer option which takes the place of the circular RA gauge above the AI, RA moves to the bottom of the AI as digital output only (737, might be different on other types).

[Lord Spandex Masher]

Like Dan said, it's not really Alpha as that is defined, aerodynamically, as the angle between the chord of the wing and the freestream airflow.

As the angle of incidence varies along the span of the wing so does Alpha.

[Winnerhofer]

Is AOA indicator still available on Airbus i.e. PFD-integrated and not separate like early A320s?

[Kefuddle]

Chris,
The difference between Pitch and FPA certainly gives a rough guide to AoA, particularly changes of AoA. As has been said by others, it should be correct in still air, but becomes increasingly inaccurate as the headwind or tailwind component increases. That's because FPA is in relation to the earth, not the airmass. (So vertical movement of the airmass, particularly a microburst, will also cause inaccuracy.)
Thanks for that, that's cleared up the confusion for me.

Regarding turbulent air, mictorbursts etc. I imagine one would experience large transient changes which I don't think would be particularly useful. The rise and fall of the barbers pole would probably provide the best awareness or critical AoA and given that TOGA FD guidance will attempt to maximise climb performance possibly at intermittent stall warnings averting one's gaze to an AoA indicator would probably not be all that helpful.

We have the AoA indicator on he HGS (737). But then we know what power settings and pitch attitude combination to use. Without specific practice/training on adjusting speed and pitch with sole reference to the AoA would anybody actually use it? Maybe as a crosscheck as long as you it doesn't then become confusing in an unusual situation.

[BARKINGMAD]

"I've never seen........"

Probably because the tight-fisted beancounters who had the FINAL SAY , over the heads of your flight ops and training requirements, on what would be bolted into your future 'frame, decided to pass on that option.

What do you think the AOA probes on most modern shiny jets measure?

The info is there, the guage/dial/EFIS Iinterface is just not there because THEY don't think it's useful/safer/necessary.

An engineer could correct me, but you might even find the wiring and the multi-connector plug (hopefully) safely tied up behind your instrument panel(s). All that's needed is a suitably placed hole and tens of thousands of local currency to your friendly xAA to certify it's fit for use.

Simples! :)

[Winnerhofer]

So does BUSS have adequate info to substitute for an AOA display?
What's Boeing's answer to BUSS?

[Denti]

Sadly the BUSS seems to be cheap enough that it is practically a standard equipment, whereas the boeing AoA indicator seems to be so expensive that nearly no airline selects it.

[vilas]

OK 465
What FPV are you talking about? Can you explain that? BUSS uses angle of attack information through IR switches instead of ADRs but there is no FPV.

[OPEN DES]

FPV is never purely inertial. (Apart from the mod you mentioned earlier possibly, dont know tbh)
In all other cases FPV uses Vzbi (baro-inertial V/S) as the input, same as V/S on the PFD under normal circumstances.
Hence the UAS (unrel air speed) procedure mentions not to use the FPV whenever air data is affected.
A question (slight thread creep) for the more knowledgeable among us:
Since what mod of the BUSS does the a/c revert to direct law with a subsequent reversion to alternate law once the flaps are selected??

Thanks

[OPEN DES]

Ok that clears things up.
I was always under the impression that when Vzbi wasn't available that AoA vs pitch was used to provide 'degraded' FPAair data to the FPV (relative to air rather than geometric).
In the sims i use when we fly with the BUSS the FPV flag shows up which implies that there is no inertial FPV. Since what mod is a pure inertial FPA available to provide data to the FPV?
Thanks!

[A33Zab]

MOD 202164 (A330)
MOD 153528 (A320)

The FPV is based on the FPA.
When ADR data is not available the baro-inertial parameter (Vzbi) is missing to calculate the 'classic' FPA. (FPA = arc tan(Vzbi/GS)

After the mod, if the baro-inertial is not available, this parameter is replaced by GPIRS (a mix of Inertial and GPS pos data)
This FPA is called the hybrid FPA.

Link to previous post (http://www.pprune.org/tech-log/531691-airbus-flight-path-angle-2.html#post8266520)

[vilas]

OK465 &A33Zab
I saw the MOI but in UAS procedure FPV plays no part what so ever. You go by memory items then QRH, ECAM and QRH again. Below 20000 with all ADRs OFF you just fly the green.

[BARKINGMAD]

...........Ladies & Gentlemen of the jury, l repeat the question yet again.

Has the THS position check been included yet in the UAS recall items?

And if not, why not?

Refer to accident reports various, exhibit #94 etc etc.......:confused: