A question on Airbus landings

I've heard that in FBW Airbuses, if your sink rate on finals is low for
whatever reason, the computers might not consider it to be a landing at
all, and might actually prevent reverser deployment and even inhibit
brake application on the landing roll?

Thanks in advance,

Ramapriya

Google the term "Radar Altimeter"

wrote:
I've heard that in FBW Airbuses, if your sink rate on finals is low for
whatever reason, the computers might not consider it to be a landing at
all, and might actually prevent reverser deployment and even inhibit
brake application on the landing roll?

Thanks in advance,

Ramapriya

wrote:
I've heard that in FBW Airbuses, if your sink rate on finals is low for whatever reason,
the computers might not consider it to be a landing at all, and might actually prevent
reverser deployment and even inhibit brake application on the landing roll?

Dave S wrote:
Google the term "Radar Altimeter"


I assume that I didn't convey myself adequately because I wasn't asking
about what the aircraft use in detecting terrain.

My question was if in a low sink rate situation - possibly a flatter
profile during finals (a no-flaps situation) or you came in slower and
touched down gently at the initial section of the touchdown roll, does
FBW technology prevent reverser deployment until too late? When I first
read about it, it struck me as the exact opposite of a safety feature
(if at all it's that) because these are the situations when you'd need
reversers the most. I also similary wondered about brakes too, and
whether onboard computers can (or do) inhibit application in some
circumstances.

And I hope this isn't what happened yesterday at Irkutsk.

Ramapriya

And I hope this isn't what happened yesterday at Irkutsk.


Repeat after me: Not all Airbusses are FBW. Not all Airbusses are
FBW...

Besides that, no, your scenario is not a valid one.

--
Thomas Borchert (EDDH)

In article om,
wrote:

I assume that I didn't convey myself adequately because I wasn't asking
about what the aircraft use in detecting terrain.

My question was if in a low sink rate situation - possibly a flatter
profile during finals (a no-flaps situation) or you came in slower and
touched down gently at the initial section of the touchdown roll, does
FBW technology prevent reverser deployment until too late? When I first
read about it, it struck me as the exact opposite of a safety feature
(if at all it's that) because these are the situations when you'd need
reversers the most. I also similary wondered about brakes too, and
whether onboard computers can (or do) inhibit application in some
circumstances.


I think you are referring to an A320 accident that happened awhile back.

http://www.savive.com.au/casestudy/warsawa320.html and
http://sunnyday.mit.edu/accidents/warsaw-report.html have the details.

Basically, it landed fast, and with a tailwind, didn't get weight
on the wheels, and the runway was wet so the wheels didn't spin
up, but hydroplaned instead. Weight on wheels is needed for thrust
reversers to be enabled, and wheel spin is needed for brakes.

This accident, and many many similar ones, are pilot training issues
more then aircraft systems issues.

John
--
John Clear - http://www.clear-prop.org/

I've heard that in FBW Airbuses, if your sink rate on finals is low for
whatever reason, the computers might not consider it to be a landing at
all, and might actually prevent reverser deployment and even inhibit
brake application on the landing roll?


You may be referring to the accident in Warsaw some years back. It was
the gear switches that didn't report landing, IIRC. It makes absolutely
no sense to connect landing detection to sink rate on final.

As for the incident in Russia yesterday, the A310 is not FBW.

--
Thomas Borchert (EDDH)

Thomas Borchert wrote:
I've heard that in FBW Airbuses, if your sink rate on finals is low for
whatever reason, the computers might not consider it to be a landing at
all, and might actually prevent reverser deployment and even inhibit
brake application on the landing roll?


You may be referring to the accident in Warsaw some years back.

Yes Thomas, I was.

It was the gear switches that didn't report landing, IIRC. It makes absolutely
no sense to connect landing detection to sink rate on final.

Pardon my ignorance but aren't the two connected, in the sense that
you'd touch down lightly if your sink rate is lower?

Ramapriya

Pardon my ignorance but aren't the two connected, in the sense that
you'd touch down lightly if your sink rate is lower?


Yes, but if you are down, you are down, i.e. the gear is compressed by
the weight of the plane. The problem in Warsaw was that the wheels
didn't start spinning because of aqua planing.

And just to make sure the point gets across: The Airbus 300 and 310
(the early models) are not FBW. The 320 and its derivatives, as well as
the 330 and 340 (and 380) are. As is the Boeing 777.

--
Thomas Borchert (EDDH)

The switch on a main gear strut is called the "Squat Switch". It's
position is used for lots of things on airplane. Pilot can by pass the
"squat" switch if needed in cockpit, ie bypass the "Squat" switch to
pull the gear up on the ground.

Haven't seen the wiring diagram but would guess that reverse thrust
would not be available until you had activation of "Squat" switch, ie
no reverse thrust until you are on the ground.

All the current birds have ASB. Failure in that system (very rare)
prevents any braking.

Lots of what ifs.

Big John

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On Mon, 10 Jul 2006 13:46:20 +0200, Thomas Borchert
wrote:

I've heard that in FBW Airbuses, if your sink rate on finals is low for
whatever reason, the computers might not consider it to be a landing at
all, and might actually prevent reverser deployment and even inhibit
brake application on the landing roll?


You may be referring to the accident in Warsaw some years back. It was
the gear switches that didn't report landing, IIRC. It makes absolutely
no sense to connect landing detection to sink rate on final.

As for the incident in Russia yesterday, the A310 is not FBW.

Big John wrote:


Haven't seen the wiring diagram but would guess that reverse thrust
would not be available until you had activation of "Squat" switch, ie
no reverse thrust until you are on the ground.


It doesn't sense wheel spin up?