Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

A320 x A330 Alpha Floor Activation During Cruise

Tech Log The very best in practical technical discussion on the web

A320 x A330 Alpha Floor Activation During Cruise

Old 27th Sep 2012, 11:57
  #1 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
A320 x A330 Alpha Floor Activation During Cruise

Here is the scenario:
- You are in flight, everything is normal. You are cruising leveled at FL390 and the MAX FL is FL390. You shut an engine off using the master switch and just watch what happens without taking any actions. For both the A320 and the A330 the speed will start to drop as the aircraft tries to keep leveled flight.


My question is: will alpha floor activate for the A330? How about for the A320?
konde_landi is offline  
Old 27th Sep 2012, 15:58
  #2 (permalink)  
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
before that, AP will trip. Then I don't know what comes first, in that scenario, if high aoa protection or alpha floor.
Microburst2002 is offline  
Old 27th Sep 2012, 17:23
  #3 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
Yeah. For the A330 here is the sequence:

1-) Aircraft start decelerating.
2-) At Alpha Prot autopilot disengages.
3-) Aircraft start descending between Alpha Prot and Alpha Max.
4-) As you did not touch the thrust levers, the operating engine thrust is limited by the position of the lever in the CLB detent.
5-) Alpha floor is not activated, as it is inhibited above M 0.53 for the A330.

I repeat my question:
How about for the A320? In the same scenario, will alpha floor be activated?

Last edited by konde_landi; 27th Sep 2012 at 17:24. Reason: spelling
konde_landi is offline  
Old 27th Sep 2012, 17:29
  #4 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
Microburst,

But you said "before that the AP will trip". Before what? Before alpha floor activation? Then you must be talking about the A320, since for the A330 alpha floor does not activate under those circunstances.

And that is my question: will alpha floor activate in this case for the A320? If it does activate that is indeed on great operational difference between the two acft.
konde_landi is offline  
Old 27th Sep 2012, 19:15
  #5 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by konde landi
3-) Aircraft start descending between Alpha Prot and Alpha Max.
4-) ...
5-) Alpha floor is not activated, as it is inhibited above M 0.53 for the A330.
Re (3): Would it not maintain Alpha Prot?

EDIT:: At Alpha Prot the flight control law changes from an Nz command law to an alpha command law. The commanded alpha is Alpha Prot for sidestick neutral, and Alpha Max for sidestick fully back. Alpha floor is not activated because the alpha threshold for its activation is not reached. At some point in the descent to the single-engine ceiling with AoA=Alpha Prot the speed may drop below M 0.53 .

Last edited by HazelNuts39; 27th Sep 2012 at 19:57.
HazelNuts39 is offline  
Old 27th Sep 2012, 20:15
  #6 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
HazelNuts39,

Totally agree. You went deeper on the explanation and it was perfect. That's exactly how it works for the A330. At sometime the speed is gonna drop below M 0.53 and alpha floor will be activated. Alpha floor however will not be triggered AT cruise flight level, it will be triggered at some point during descent.

Will the same happen for the A320? The "M0.53 rule" does not appear on the manual for the A320. Knowing that, will alpha floor be activated AT cruise level for the A320?

Last edited by konde_landi; 27th Sep 2012 at 20:17.
konde_landi is offline  
Old 27th Sep 2012, 21:27
  #7 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
At sometime the speed is gonna drop below M 0.53 and alpha floor will be activated.
With the sidestick remaining in neutral the airplane stays at Alpha Prot and alpha floor will not be activated.
HazelNuts39 is offline  
Old 27th Sep 2012, 22:26
  #8 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
HazelNuts39,

I got that. The aircraft will enter alpha floor only if you give a further pitch up input AND you are below M.053 on the A330, which is gonna happen at somepoint during the single engine descent at alpha prot (in the proposed scenario).

ON THE A320, if I shut down an engine during cruise at FL390, don't take any actions, wait for the aircraft to reduce to alpha prot, and give a further pitch up input to the sidestick, will alpha floor activate at FL390?
konde_landi is offline  
Old 28th Sep 2012, 01:06
  #9 (permalink)  
 
Join Date: Jun 2009
Location: Australia
Posts: 2,167
Likes: 0
Received 2 Likes on 2 Posts
Yes Alpha floor should only activate if you are below .53 Mach, AOA protections are active AND Sidestick deflection is more than 14 deg back.

From the A330 FCOM 1

Normal Law Pitch protection:-

HIGH ANGLE OF ATTACK PROTECTION

Under normal law, when angle of attack becomes greater than Alpha prot, the system switches the elevator control from normal mode to a protection mode in which the angle of attack is proportional to the sidestick deflection. That is, in the Alpha prot range, from Alpha to Alpha max, the side stick commands Alpha directly. However the angle of attack will not exceed Alpha max, even if the pilot gently pulls the sidestick all the way back. If the pilot releases the sidestick the angle of attack returns to Alpha prot and stays there.


In addition to that it goes on to say:-


Alpha FLOOR is activated through autothrust system when :
Alpha is greater than a threshold depending on the aircraft configuration, the ground speed variation, and the difference between ground speed and air speed or,
Sidestick deflection is above 14 deg and:
pitch altitude is greater than 25 deg,
or AOA protection is active

Alpha FLOOR inhibition: (Refer to 1.22.30).

Last edited by nitpicker330; 28th Sep 2012 at 01:46.
nitpicker330 is offline  
Old 28th Sep 2012, 01:18
  #10 (permalink)  
 
Join Date: Jun 2009
Location: Australia
Posts: 2,167
Likes: 0
Received 2 Likes on 2 Posts
The ALPHA FLOOR protection is triggered when the FMGECs receive a signal elaborated by the PRIMs. This signal is sent when the aircraft angle of attack is above a predetermined threshold function of the aircraft configuration. The A/THR is automatically activated and commands TOGA thrust regardless of thrust lever positions. This protection is available from lift off to 100 feet RA in approach. Following indications are then provided : A-FLOOR on the FMA and on the EWD as long as Alpha floor conditions are met TOGA LK on the FMA when the aircraft leaves the Alpha floor conditions. TOGA thrust is then frozen A FLOOR and TOGA LK are displayed in green and surrounded by an amber flashing box. In order to cancel the ALPHA FLOOR or TOGA LK thrust, disconnect the A/THR.


Alpha floor is inhibited:-
in case of engine failure with flaps extended
in case of engine failure with derated TO selected
in case of a single outer engine failure, with the flaps extended. (A340)
in case of a single outer engine failure, with derated TO selected. (A340)
in case of a dual engine failure on the same wing. (A340)
below 100 feet at landing
above M.53

Alpha Floor protection is lost in case of A/THR

Last edited by nitpicker330; 28th Sep 2012 at 01:38.
nitpicker330 is offline  
Old 28th Sep 2012, 01:28
  #11 (permalink)  
 
Join Date: Jun 2009
Location: Australia
Posts: 2,167
Likes: 0
Received 2 Likes on 2 Posts
So, Engine failure in cruise and your speed drops to Alpha Prot:-

1/ the A/P disconnects
2/ the Pitch reduces to keep Alpha Prot AOA
AND Alpha floor will activate if you are pulling back more than 14 deg, UNLESS inhibited.

Last edited by nitpicker330; 28th Sep 2012 at 01:44.
nitpicker330 is offline  
Old 28th Sep 2012, 05:36
  #12 (permalink)  
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
In the 320, I guess it depends on the deceleration rate.

If it was very fast it could hit the alpha floor threshold, whereever it is... If it is not fast, high aoa protection will keep the airplane at alfa prot, so no alpha floor activation would occur
Microburst2002 is offline  
Old 28th Sep 2012, 08:52
  #13 (permalink)  
 
Join Date: Jun 2009
Location: Australia
Posts: 2,167
Likes: 0
Received 2 Likes on 2 Posts
I'm sure it would be the same on the 320.
nitpicker330 is offline  
Old 28th Sep 2012, 09:21
  #14 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
In the 320, I guess it depends on the deceleration rate. If it was very fast it could hit the alpha floor threshold, whereever it is...
In the conditions stated in the OP, the A330 decelerates at about 0.04 Mach per minute.
HazelNuts39 is offline  
Old 28th Sep 2012, 12:56
  #15 (permalink)  
Thread Starter
 
Join Date: Jul 2008
Location: Sao Paulo
Age: 41
Posts: 8
Likes: 0
Received 0 Likes on 0 Posts
On the A320, alpha floor is not inhibited above M0.53. In this case, we could have alpha floor activation at FL390 (example). That is my understanding of the whole thing.

I done it on the simulator for the A330 and alpha floor does not activate whatsoever until the aircraft is at an altitute that allows flight at M0.53.

I'm sure the rate of deceleration does not play a role here, since the alpha floor trigger is AOA, and not a "projected time to reach alpha max based on current deceleration rate assuming you are gonna give further pitch up input when you reach it".

I found nothing so far written on the manuals that convinces me that alpha floor will not activate at cruise FL for the A320. If someone experienced this situation or could try it on the sim it would be great!
konde_landi is offline  
Old 28th Sep 2012, 15:17
  #16 (permalink)  
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
What does trigger alpha floor, anyway??

Deceleration rate matters, because by the time high aoa protection is able to arrest the loss of speed, you will reach alpha prot or not depending on how quick the protection was

Last edited by Microburst2002; 28th Sep 2012 at 15:19.
Microburst2002 is offline  
Old 28th Sep 2012, 17:56
  #17 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Microburst2002
Deceleration rate matters, because by the time high aoa protection is able to arrest the loss of speed, you will reach alpha prot
High AoA protection does not arrest the loss of speed, it does arrest the increase of AoA, which in the proposed scenario is relatively slow: from approx. 3 degrees in cruise to alpha prot of about 6 degrees in about four minutes.
HazelNuts39 is offline  
Old 28th Sep 2012, 19:34
  #18 (permalink)  
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,916
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by konde_landi
4-) As you did not touch the thrust levers, the operating engine thrust is limited by the position of the lever in the CLB detent.
As you put it here, we can assume A/THR is ON. This was not specified in the initial scenario.
Point 4 is of no importance as there is no 'thrust limitation' at FL390 since climb thrust is nothing short of MCT or TOGA. Nothing to gain to have alpha floor anounciated on the FMA as thrust on the remaining engine is already at its max possible output.
As mentioned earlier, the important point is the alpha prot activation preventing a further AoA increase.

It is still a good scenario to think about.
CONF iture is offline  
Old 28th Sep 2012, 22:21
  #19 (permalink)  
 
Join Date: Mar 2000
Location: Sunrise Senior Living
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
What actually happens in the 320 sim is that the speed slowly comes back to V alpha prot, the autopilot disengages, tha ac then pitches down to regain/maintain V alpha prot and it drifts down at that. While flashing LVR MCT at you!
mcdhu
mcdhu is offline  
Old 29th Sep 2012, 05:07
  #20 (permalink)  
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
Exactly

High aoa protection pitches the airplane down to prevent aoa from exceeding alpha prot (sidestick neutral)

If the deceleration rate is very high, the aoa will reach a higher value, maybe avtivating alpha floor. If it is slow, the protection doesn't let the aoa to trigger alpha floor.

With an engine in MCT, deceleration rate should be relatively slow, even at max alt. If we did the experiment of retarding both thrust levers maybe alpha floor would be triggered
Microburst2002 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.