A320 AOA on Approach

[RvB]

Does anyone have experience with the usage of AOA values via alpha callups in case of unreliable airspeed indication resulting in mere pitch and power flying on approach in an A319/320/321 ?
Thought it could be helpful to use this information in addition to other ADR+AUX-Speed indication substitutes.

Cheers RvB

[gearpins]

.....and how would that help?...:confused:

[EMIT]

Primary are pitch and power. Set those right and you will stay safely in the air.

If you know how to find AOA in the maintenance pages of the MCDU, the AOA value may confirm that your pitch and power setting are performing correctly.

Trying to control the aircraft through AOA will be awkward: the MCDU is not directly in your direction of flight, where you would want to have your line of vision.
More importantly though, if you fly the correct AOA, but with too little power set, you will descend.
Trying to control the flightpath with AOA (alone) will easily lead to chasing the AOA value, giving an unsteady flight path.
In other words, pitch and power are the controlling factors.

Don't be fooled by fighter jets, where AOA is used rather than speed, during approach: the symbology is in the HUD and flightpath is then controlled with the Flight Path Vector (akin to the Airbus Bird), also in the HUD. Also, the short, stubby wings have different AOA versus speed ratio's than the slender wings of commercial airliners.

[RvB]

Thanks EMIT, good points !

[Fargoo]

Don't forget your unreliable airspeed my be caused by a faulty AOA sensor.
Something to bear in mind :ok:

[A-3TWENTY]

What about UNRELIABLE SPEED INDICATION paper checklist?

[JABBARA]

I do not have an exact figure for A 320 but the following values which I have recorded some time ago for A 330-200 on a 3 degree GS ILS. The values are independent of weight. You can find the relevant page on MCDU (the way to find the page for all A 330s it may not be same)
ACMC>ALPHA>ALPHA MENU DISPLAY> now write Alpha Call-up code "AOA", you will see the AOA values calculated by two different sensor)

Full Flap 6 degree
F3 7.5 degree.

I believe the values for A 320 shuld be close to these values.

Yes MCDUs are not in the direction where PF is looking at final approach, but at least PNF can confirm that PF is handling the airplane at correct speed as reading these values.

In my old airforce days with T-38 , there was neither HUD nor FPV indicator. The cockpit was quite conventional cockpit, but on dashboard there was a little gadget showing 3 lights, with green circle in the middle. We used to land without calculation approach speed for any weight. Simply maintain a speed so that green light comes on. So in my consideration in a worst case scenario, at least for confirmation, AOA value may be used.

In fact Airbus has an option on PFD simply relies on AOA, which can be used in Unreliable speed Case. The following is an extract from Airbus safety First Magazine Issue No 5.

"Back Up SpeedScale (BUSS). In order to decrease the crew workload in case of unreliable speed, Airbus has developed the Back-Up Speed Scale (BUSS) that replaces the pitch and thrust tables. The BUSS is optional on A320/A330/A340. It is basic on A380, being part of the ADR Monitoring functions.This indication is based on angle of attack (AOA)sensor information, and is therefore not affectedby erroneous pressure measurements.The BUSS comes with a new ADIRU standard (among other new system standards), where the AOA information is provided through the IRs and not through the ADRs. This enables selecting all ADRs off without loosing the Stall Warning Protection. The AOA information provides a guidance area inplace of the speed scale. When the crew selectsall ADRs OFF, then:
•The Back-Up Speed Scale replaces the PFD speed scale on both PFDs,
•GPS Altitude replaces the Altitude Scale on both PFDs.
The Back-Up Speed Scale then enables to fly ata safe speed, i.e. above stall speed and below maximum structural speeds, by adjusting thrust and pitch.

The BUSS will be displayed once all ADRs areswitched OFF. Therefore, on aircraft that have the BUSS, when the flight crew cannot identify the faulty ADR(s) when performing the troubleshooting,or when all ADRs are affected, the flight crew willswitch OFF all ADRs, and will fly the green area ofthe BUSS. However, if the safe conduct of the flight is affected,the memory items must still be applied beforetroubleshooting.As the BUSS is associated to the ADR monitoringfunctions, some unreliable speed situations canbe automatically detected (e.g. new ECAM warning“NAVADR 1+2+3 FAULT”), and some ECAMprocedures will lead to the BUSS activation byrequesting to switch OFF all ADRs."

[Dan Winterland]

An AOA guage is an option on the A320.

I used to instruct on a military aircraft with an AOA indicator, and the apporach AOA inditaor which woked with the gear down as Jabarra describes. It's a very useful gadget and those of us who flew the Tucano found we used it a lot. We had a problem with the ASIs failing due to disturbed airflow over the staic vents while spinning invered. It happened to me twice. The official way of getting it back on the ground in this situation was to fly a formation approach and landing, but the second time it happened to me I flew an approach using the AOA guage which worked fine.

Interestingly, Air data Recorders record AOA and accident investigators always comment on AOA in handling incidents. But not many people think it's important for the pilots to know!

[RvB]

I, more than once, read values around 5 Degrees on an 3 Degree GS/Config Full in an A320.