Ask The Pilot

[juddles]

Yellow pages, anyone?

I was more picturing some hero throwing one of those soft orange traffic cones under the wheel, and then being surprised when it got flattened and failed to stop the 450 ton object from continuing on its path.

 

[jb747]

Which is why there should be somebody in the coughpit, with the hydraulics (or at least those used for braking) powered up.....

Applying the brakes with the aircraft rolling backwards can be problematic though...

 

[flychrisfly]

Applying the brakes with the aircraft rolling backwards can be problematic though...

Why is that? What's the difference between breaking on a forwards moving plane to a backwards moving plane (apart from the absence of a rear view mirror)?

 

[richie9x]

Why is that? What's the difference between breaking on a forwards moving plane to a backwards moving plane (apart from the absence of a rear view mirror)?

I would expect if the pilot braked too hard while traveling backwards they would soon have a very good view of the sky, a bit of damage to the tail and a please explain meeting with management.

 

[equus]

Why is that? What's the difference between breaking on a forwards moving plane to a backwards moving plane (apart from the absence of a rear view mirror)?

Think about what happens when you hit the brakes when moving at any speed. Going forwards, the effect will be to have the nose squat down - which is fine, as there is a nose wheel to hold it up. Going backwards, there is no wheel under the tail, and you will risk a tail strike as the whole thing tips over.

 

[jb747]

And, because the C of G could conceivably be quite aft with the aircraft on the ground (further aft than it would be allowed for flight), it might take a very little touch of the brakes for that to happen. As pilots, we never apply the brakes whilst going backwards...and a drawbar failure would be about the only thing that would make us do so.

 

[Simsy85]

And, because the C of G could conceivably be quite aft with the aircraft on the ground (further aft than it would be allowed for flight), it might take a very little touch of the brakes for that to happen. As pilots, we never apply the brakes whilst going backwards...and a drawbar failure would be about the only thing that would make us do so.

You ever seen someone do that? nothing like an A380 poppin a wheelie....

 

[jb747]

Thankfully no.

You do occasionally see images of what happens when the C of G goes too far aft, normally with freighters whilst being loaded.

 

[Simsy85]

You ever seen someone do that? nothing like an A380 poppin a wheelie....

something like this......

 

[markis10]

Some aircraft are very CofG sensitive

Photos: McDonnell Douglas MD-11(F) Aircraft Pictures | Airliners.net

 

[ozmille]

Which is why there should be somebody in the coughpit, with the hydraulics (or at least those used for braking) powered up.....

That is what happened in BRU in 2004 when this Thomas Cook plane was pushed back empty and got disconnected and rolled into the airport building. At least I got to see the Beluga

 

[Stephen65]

I had a curious experience flying on a JQ flight SIN-MEL earlier this year. We arrived in MEL about dawn and were taxiing up to connect to the airbridge when the aircraft came to an abrupt stop about 20' short. The captain came on the PA and said that for some reason the aircraft couldn't connect to the airbridge and that even once the issue was resolved then according to MEL airport rules the aircraft was not allowed to resume taxiing to the tunnel and would have to be towed in. There was then a prolonged wait until a tow vehicle with the right connector turned up and pulled us in. What's the rationale behind not allowing the aircraft to resume taxiing?

 

[jb747]

I had a curious experience flying on a JQ flight SIN-MEL earlier this year. We arrived in MEL about dawn and were taxiing up to connect to the airbridge when the aircraft came to an abrupt stop about 20' short. The captain came on the PA and said that for some reason the aircraft couldn't connect to the airbridge and that even once the issue was resolved then according to MEL airport rules the aircraft was not allowed to resume taxiing to the tunnel and would have to be towed in. There was then a prolonged wait until a tow vehicle with the right connector turned up and pulled us in. What's the rationale behind not allowing the aircraft to resume taxiing?

Sounds to me like the aerobridge wasn't actually parked in the correct position. Even with outside guidance, if it isn't in the fully parked position, then you do not go near it.

The heavies that park opposite Virgin are not allowed to restart under power if they stop short of the gate, but that's because their jet blast blows back onto Virgin. That rule has been in place since Ansett's days. I've never heard of any such rules applying to the smaller aircraft, but I've also not operated onto a Melbourne domestic gate in a long time. If there's nothing behind the aircraft, and the bridge is correctly parked, I can't see the issue.

 

[harvyk]

And, because the C of G could conceivably be quite aft with the aircraft on the ground (further aft than it would be allowed for flight), it might take a very little touch of the brakes for that to happen. As pilots, we never apply the brakes whilst going backwards...and a drawbar failure would be about the only thing that would make us do so.

So when a plane is being reversed by a tug, does the tug provide any braking? Or does the tug simply let the plane come to a standstill of it's own accord (eg when momentium runs out)...

 

[jb747]

So when a plane is being reversed by a tug, does the tug provide any braking? Or does the tug simply let the plane come to a standstill of it's own accord (eg when momentium runs out)...

The tug does all of the pushing/pulling and braking. Many aprons have quite a slope, and the aircraft won't stop by itself.

 

[anat0l]

This might well and truly be a naive question with an obvious answer, but for QF/JQ which use MEL T1... now how is best to describe this...

MEL T1 can be imagined as a kind of "U" shaped structure - the two sides of the "U" are the two piers off the main part of the terminal building (one pier is Gates 1-11 or something like that; the other is Gates 12-30 or something like that). "Inside" the "U" - that is, between the two piers - are a number of gates where pushback is usually quite a lengthy procedure. I see aircraft being pushed out of their gate, all the way back out of the "U" and finally into a position which is clear of the U and perpendicular to the pier containing the high-numbered gates (i.e. you can see gates 25-30 - the turboprop gates - if you are on the left hand side of the aircraft when it is pushed back to this position).

What kinds of considerations or restrictions make it necessary for pushback to have to go this far at MEL T1? Or is it possible to make do with a shorter pushback (albeit perhaps not as safe / smaller contingency, etc.)?

Are there other airports around the world that necessitate a similarly long pushback procedure?

 

[Flying Fox]

You ever seen someone do that? nothing like an A380 poppin a wheelie....

Balance it out with some forward thrust

 

[jb747]

Balance it out with some forward thrust

Two problems...firstly the engines aren't normally running at that point, and secondly, the couple might not be in the direction you imagine.

 

[jb747]

What kinds of considerations or restrictions make it necessary for pushback to have to go this far at MEL T1? Or is it possible to make do with a shorter pushback (albeit perhaps not as safe / smaller contingency, etc.)?

Two issues for those bays. Firstly, the ones in close to the terminal don't have enough room available to push the aircraft back so that the tail is facing the terminal.

Secondly, and more important, the level of thrust required to start the aircraft moving is a lot higher than needed to keep the aircraft rolling. These thrust levels are dangerous if the blast impinges upon another aircraft, a building, or workers.

Are there other airports around the world that necessitate a similarly long pushback procedure?

Anywhere that you are parked within the 'U' will normally mean the jets (especially the larger ones) will need to be pushed back until on an adjacent taxiway. LA. JFK. Numerous places.

 

[reductionist]

Rejected Take Off

Hi JB.

One of the multiple delays I experienced on SYD-MEL yesterday was a hold-up just prior to take off.

The captain announced to us that the aircraft ahead of us rejected it's take off and a runway inspection was required before we could proceed.

So, my question is, under what circumstances is a runway inspection required?

My initial thoughts were that perhaps the aircraft spotted or hit some debris on the runway, or they had a tyre blow out or something.

Then I wondered if this is standard procedure for all rejected take offs?

i.e. Could a usually innocuous warning light on take-off potentially be caused by a seemingly unrelated part falling off the plane?