Question about windshear Go/Around

[tango4]

Hi, just a quick question for pilots here.
I recently attended a briefing regarding a missed appraoch incident we had at LFPG with an aircraft on Go Around following a windshear on short final.
The aircraft happened to be an Embraer E Jet. According to the pilot report, when pushing the TOGA button following a Windshear warning, the aircraft "knows" it is a windshear and commands a specific roll mode(wings level I think) instead of the usual guidance.


Here is the confirmation I am looking for:
On Boeing and Airbus aircraft, there is NO DIFFERENCE system wise between a normal go around and a windshear go around. When I press TO/GA (or push the throttle in the final detent on Airbus), I will always have the same guidance even if I press it following a windshear alert. Only the procedure part is different (you don't change airplane config, etc etc).

Could you please confirm the above statement is true ?


All the best.


Charles

[andmiz]

Yes.... and no; the guidance you receive on the 747 is different.  In a go-around scenario, the AFDS will pitch for 15 degrees or just slightly the PLI's, and once an appropriate rate of climb is achieved (actually, as it transitions through  600fpm to achieving at least 1200fpm all engine or 0-600fpm engine out), it will begin a transition from this pitch mode to a speed mode. 

However since an appropriate rate of climb is perhaps not achieved in a wind shear scenario, that AFDS guidance will continue.  So it doesn't 'know' per se, but the performance criteria allowing it to transition through the TOGA guidance is not achieved. 

[tango4]

Thanks a lot for your answer.


Just to make sure I understood correctly, you are talking about vertical guidance only, and the difference would be a "side effect" of potentially not meeting the criteria for the "end of the sequence".


But the lateral guidance is the same, trying to maintain the track of the aircraft at the moment the button was pushed, not a "wings level" as seems to be the case on the Embraer. Is that correct ?

[Hardy Heinlin]

As far as I understand the term "track" in the context of the AFDS TO/GA mode, AFDS "track" is not a geographically fixed track but a floating track, i.e. aircraft heading plus wind correction angle. E.g. when the crosswind component changes, the aircraft will just change its WCA, but it will not return to the geographic track. It's geographically floating, similar to HDG HOLD. When a turbulence occurs, the HDG HOLD will restore the memorized heading, but it will not return to the previous geographic track. It just banks back to the memorized HDG (HDG HOLD) or memorized TRK (TO/GA), it will never overbank to return to the route; thus it's nearly the same effect as the wings level command on the 747-200. As we know, the 744 has no wings level switch anymore on the MCP. But it has HDG HOLD and TO/GA.


|-|ardy

[tango4]

That is basically how I understand it.
But the "track guidance" offers a bit of protection against side drift.
In case of windshear scenario, it is frequent to get a vertical wind gradient. So I guess the aircraft will attempt to compensate for the changing wind (but as you say, if you drifted a bit, the aircraft will not get back to the runway centerline , but at least avoid drifting further).
On the Embraer it seems it is pure wings level initially followed by HDG SEL. From what I understood in the pilot report, they preselect a HDG in the window when beginning the approach that takes into account the wind. But it is very approximate as you can guess.
In the event I was mentioning, the Embraer drifted rather significantly. And I remember seeing the same with a Q400 during a storm in winter 2019.

[BEL747]

Hello Everybody,

This question relates more to the aircraft and ATHR system logic than to the Windshear (WS) escape manoeuvre itself.

I checked the FCOM already but could find the answer.

From flying both the sim (PSX or a FFS) and the real aircraft, I could notice that a SINGLE push of TOGA during an approach (AP ON or OFF) does not have the same result on ATHR command depending on the situation:

- during a normal approach, 1 push of TOGA = N1 for minimum 2000ft/min ROC
- in reactive WS condition on approach, 1 push of TOGA systematically commands a N1 close (but not equal) to max GA N1.

My question is: how is this reduce WS GA N1 calculated? What is this equal to? Another specific ROC? N1 sufficient to maintain speed with 15° pitch?

I couldn't find any information about this in the FCOM (I am talking specifically about the ATHR commanded N1 ico WS, not the TOGA pitch guidance for WS).

If anybody has any information on this, wether documented or not, or even just a personal feed back even, I would be happy to read it .

Thank you in advance,

Best Regards,

BEL747

[Hardy Heinlin]

Hello,

in PSX, when THR engages with TO/GA go-around, the thrust will automatically increase until the system detects that the current thrust will provide at least 2000 fpm (the system considers the current V/S and the V/S acceleration to avoid excessive overshooting).

Now when this system is operating during a windshear, the climb rate is very low due to the windshear, and as the climb rate will rise very slowly with the increasing thrust, the thrust may reach the THR REF limit way before the climb rate approaches the 2000 fpm target. I don't know if the real AFDS gets windshear information from the EGPWS; in PSX this is not the case. In PSX, the THR may reach THR REF during a windshear even when the EGPWS is inoperative.

When THR is engaged and the thrust reference limit is reached, the annunciated mode word remains THR; the mode word will not change to THR REF.


Regards,

|-|ardy

[BEL747]

Hello Hardy,

Thank you for your answer.

It makes more sense now!!

That could very well be the only reason. Nothing being mentioned about a different logic and possible different ATHR logic during WS...

Thank you,

Best Regards,

BEL747