Airbus nose gear - Typically how long in air after main gear touchdown?
 

This is from an engineer. The aircraft type I’m working on, an Airbus, has thrust reversers which are able to deploy as soon as the main landing gear touches down. That’s normal so far. Thrust reverser deployment inflight is clearly undesirable, and the aircraft will produce alerts if any part of the TRU system becomes “unlocked” in flight. Unfortunately, the alert logic considers “on ground” to mean main landing gear and nose gear on ground.

You may already have guessed the issue here. Upon landing, the main gear touches down first and the thrust reversers deploy, but as the nose gear is still airborne, the alert logic considers the aircraft airborne and spews out unwanted TRU unlocked in flight messages, every single landing.

The way to stop this is to tweak the alert software to delay the unwanted alert until the nose gear has touched down and the aircraft is “on ground”.

Is there any sort of guidance as to the maximum time the nose gear can be airborne after the main landing gear has touched down? A piece of string question perhaps, but it’s for a valid reason as is hopefully explained above. Many thanks for any input.

simply:

No.

The way you land an A320 and 330 340 350 380 is different.

complicated:

A320 Touchdown you select Reverse immediately. The Nose drops and you need to slow it down by pulling the six firm 1-2 times so the Nosewheel doesn't drop to hard.

A330 touchdown of course you select the reverse immediately but you need to get the whole boogie down. you keep the nose up a little longer so that all main wheels touch the ground, and then you need to fly the nose to the ground a bit.

And it all depends a little from the auto brake, there are different softwares, old and new ones. you can fly with two AC of the same MSN number . both 5XXX for example and both may brake differently. Old ones sometimes first trigger the Automarke when Nosewheel touches down, others simply the preselected seconds after main wheel touchdown.

But you should never try to keep the nose in the air! some dudes try to airbrake the 320 keeping the nose up, this is totally wrong. but when VMU is reached the Nose will just drop very hard ...

Thanks, so using the A330 as an example:




I count 15 seconds between the main landing gear touching down and the nose gear doing likewise. Would this be considered a long time?


If there's no guidance available, fair enough. We'll delay the unwanted alert by an arbitrary duration, but it's always nice to have some rationale and point of reference.

I haven’t seen any guidance in any official document. However, while the posted video certainly shows a very smooth landing, the pilot seems to have held the nose longer than usual, so 15 seconds seems excessive.

Then again, if you really have a reverser fault, it should stay on throughout the landing run, till reverser retraction speed, which is typically 20-30 knots

In your case I’d start with an arbitrary value of, say 10 seconds and see how it works out...

i don't fly the 330 so i don't have a clue, but as an 320 driver I say thats too long, maybe compare to the auto land?


FCOM 320:

At Touchdown:
Derotation ... initiate
-lower the nose wheel without undue delay
-The PM continues to monitor the attitude

ALL THRUST LEVERS .................... REV MAX or REV IDLE
The flight crew must select reverse thrust immediately after main landing gear touchdown.

10 seconds is more than enough for normal ops. From braking performance viewpoint that filmed landing is wrong.

Why not tweak the alert logic so that the aircraft is considered 'on ground' as soon as the main wheels touch down?

"How long in air"?

Until it gets down...

The US Airways video doesn't appear to show any thrust reverse use. Most unusual.

@ Hodd,

I’m going to say the obvious....why you asking us instead of Toulouse?
You should be contacting Airbus with this if it’s a genuine question.
This sounds like a FlightSim question to me.

LAE comes on an Internet forum to seek advice before "tweaking" something that will alter the operational characteristics of the aircraft he/she is there to maintain ?

Doesn't quite ring true to me.

Thanks all, some helpful and some interesting replies.

Quote:

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Originally Posted by Easy Street (Post 10032747)

Why not tweakthe alert logic so that the aircraft is considered 'on ground' as soon as themain wheels touch down?

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That’s another option. The alert logic uses flight phases, and unfortunately “landing roll” is only reached when all landing gear is on ground. Just the main landing gear on ground is still considered “final approach”. However, it is possible to change the logic as you suggest, just a bit more work.

Quote:

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Originally Posted by DaveReidUK (Post 10032878)

LAE

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The only time I’m near aircraft is as a passenger. I’m a development engineer.

Quote:

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Originally Posted by B2N2 (Post 10032809)

why you asking us instead of Toulouse?

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Fair comment. I am dealing with Airbus engineers, but instead of presenting a problem, I try to be a little proactive and have some ideas.

but i have never seen a Rev Unlock Warning with nose wheel airborne... its clearly said in the FCOM that you'll get a slight pitch up with reversers opened.

What exactly is the problem? never change a running system. you are dealing with stuff thats not causing any problems.

try to fix ATC Datalink fault and stuff like that. thats what we hate ! no downlinks etc

It's a new aircraft type, which will be fairly obvious to guess now, and it's not an existing problem.

There's no safety issue nor would the flight crew be inconvenienced, but some engineers somewhere will have to deal with and close out the spurious alerts every single time that aircraft type lands. That's not a small problem.

I am not sure I follow your logic.
There are sensors telling the logic that the main gear is on the ground so it is OK to deploy thrust reversers. Right? So the alert logic should now have an input saying it is OK so don't raise any alerts.
Your 3rd paragraph refers to "delaying unwanted alerts until the nose gear is on the ground". If the nose gear is on the ground, you don't want any alerts, let alone "unwanted" ones.
Bottom line surely is to take the nose gear out of the process?

I think the case is:

. the normal operating technique for opening the reversers is after MLG touch-down
. the reversers open notmally, the inhibit feature is set-up that it is indeed possible as per AFM / certification
. the on-board monitoring system used by maintenance does however
- have logic that on ground = NLG
- reports a false positive of failure: reversers open before supposed to
. quite likely crews do not see any of this, their FWC is coded properly

As a consequence, for all the landings when reversers are open in a timely and correct manner (at MLG touchdown) the poor guys at MCC
- receive (string of) messages from the on-board monitoring system
- telling them the REVs did open too early, i.e. without NLG on ground
- everybody knows it's a false positive
- it's not an airworthiness issue because only the MX monitioring system is affected
- it creates HEAPS of unnecessary workload when the engineers need to formally investigate, troubleshoot and close with no fault found every single of those false-positive messages (quality control on their side).
- they'd rather be doing something productive, like fixing aeroplanes or preventig them from breaking down.

Hodd: Do I understand correctly that: You have a plan to PATCH the ground-based part of the MX monitoring system
- so that the false-positive REV UNLK before TCHDN messages would be discarded automatically
- because the root FIX in the on-board part of the MX monitoring system is just not coming (yet): A/C type either too old, too new or too unique

It should do, but the alert logic currently expects all landing gear on ground before the thrust reverser starts to deploy. This is out of sync with the aircraft thrust reverser logic which expects just the main landing gear on ground.

Sorry, I didn’t write that very well. We would delay unwanted alerts whilst the main landing gear is down but the nose gear is still airborne (aircraft “in air”, thrust reversers deployed). Once the nose gear touches down, the alert logic finally considers the aircraft on ground, and at this condition (on ground, thrust reversers deployed), there will be no alerts.

Good summary. Whilst it’s not an airworthiness issue, it would create lots of unnecessary work, i.e. two reports per landing for every aircraft whenever thrust reversers are used, if left unfixed. As this issue has been spotted at the development phase, it’s only right and responsible to fix it.

I’m not familiar with MX, but it’s a new aircraft type. My suggestion of a time delay would “mute” spurious alerts upon landing provided the nose gear touches down within the specified time. Other options such as using just the main landing gear as inputs for the alert logic are also viable. The fix would be on the aircraft software side and not ground based.

NEO or 350? Or is this top secret :)

If this is an issue "discovered" at development phase Airbus should already have it on their MISP list with a related TFU in place. Seems strange if they don't.

With enough experience, with good weather, good judgement, a long runway, no traffic behind, and appropriate conditions, a pilot might perform a leisurely landing - just for the joy of it.

Don’t shoot me...........

(The A330 stops on a sixpence once the autobrake activates).

However; the A330 landing shown is very excessive in my humble view - a few seconds between front mains landing and nose wheel touch down maybe, not 12 !! S/he delays too long the front mains landing as well.

What must be borne in mind is that when you really need to do a performance landing on a short field; can you?