Flight envelope protection...

[BigHitDH]

Hi all,

Suppose cabin crew calls you to say there is a madman running around in economy, and they need you to "throw it around a bit" so they can get on top of him; just what sort of aerobatics can you do with a modern airliner?

I'm thinking of Airbuses really:

Will the flight computers not limit how rough you can make it?
Do modern airliners set a +/- G limit that they'll let you impose on the airframe?
What about maximum bank angles?
If G limits are imposed, how do the computers resolve overspeed/stall/plunge in the ocean situations? What takes precidence?


I'd love to know!

[BigHairyBum]

Firstly it is unlikely that the cabin crew would make such a request. Assuming they do, and assuming the pilots are going to oblige then the g limits you mentioned for most airliners are typically +2.5/-1 clean and +2.0/0 with flap.

An Airbus will stop you at those limits. Most other airliners need the pilots to stop at them. An airbus will also stop you at +30 degrees and -15 degrees in pitch and 67 degrees of bank (a 2.5g level turn) assuming normal control law.

An Airbus also has high and low speed protections. At the low end of the scale you will fly into the angle of attack protection and the slowest the airbus will let you fly is V alpha max. The angle of attack protections are significantly more advanced than a standard stall warning stick shaker or pusher and would require me to write far to much for this thread.

High speed protection is more simple however. The Airbus will simply stop you sustaining flight above Vmo/Mmo by applying a pitch up bias and taking power off. It will not stop you exceeding Vmo/Mmo though as transient overshoots are permitted.

Basically if you want to fly aeros an airbus isn`t going to help.

I personally don`t think it would be wise to "throw it about a bit" anyway. You could cause more harm and chaos than you started with. Better the cabin crew seek assistance from able bodied passengers if they cannot control the fruit cake themselves.

:(

[BigHitDH]

Thanks for the detailed info.

I'm surprised by the 67 degrees bank angle, seems like an awful lot - it would certainly be unnerving to see nothing but the ground out of a pax window! :ooh:

I think the Alpha Floor protoection on the Airbuses is a great feature, are there any other aircraft that have a similar feature, or do Boeings just have the stick shaker/pusher? Also, I'm aware (I think) that the Boeing range has a maximum bank angle of 35 degrees with the autopilot engaged, is there a maximum without autopilot?

I'm also interested to read you don't think "throwing it around a bit" is a good idea. Are there any airline/airframe specific SOP's in regards to this, or is it purely down to the Captain's discretion?

Thanks again.

[Pilot Pete]

I'm also interested to read you don't think "throwing it around a bit" is a good idea. Are there any airline/airframe specific SOP's in regards to this, or is it purely down to the Captain's discretion?

Unsecured articles in the cabin. Let's say the meal/ drinks service is underway on a 747-400. That's a lot of heavy carts (that's with a 'c' not a 't' !) also being thrown around the cabin. 20 odd damaged/ maimed/ dead passengers is significantly worse than one nutter. Remember also the accountability aspect. The Captain will have to justify all his actions at the inquiry into the deaths of the several who were hit with a 50kg cart with a force of, let's say 2g.

And that doesn't even count the numerous pax who weren't strapped in themselves at the time you acceeded to the cabin manager's request to pull some 'g', or the over head bin contents etc etc..............................

Just a thought, leave it to the CC who will quickly get the assistance of some hefty pax. The Captain has to keep the big picture and pick the best course of action that protects as close to everyone as he can from injury.

PP