Ask The Pilot

[jb747]

Here are some interesting videos of a BA flight going around at Gibraltar, reportedly due to wind.

The writer ponders at the end of the post whether this may be a pilot enduced manoeuvre to counter the wind.

Could this be the case?

If so, can you explain the physics of how/why is this effective?

INSANE Video Of British Airways Plane Approaching Gibraltar In Heavy Winds - One Mile at a Time

Wow.... This is almost certainly a PIO, or pilot induced oscillation. A stuff up in other words. Sometimes it's best just to put the controls in the middle for a while, and let the aircraft's inherent stability sort out it's own act.

Pilot-induced oscillation - Wikipedia

 

[harvyk]

Here are some interesting videos of a BA flight going around at Gibraltar, reportedly due to wind.

The writer ponders at the end of the post whether this may be a pilot enduced manoeuvre to counter the wind.

Could this be the case?

If so, can you explain the physics of how/why is this effective?

INSANE Video Of British Airways Plane Approaching Gibraltar In Heavy Winds - One Mile at a Time

I feel queasy just from watching that video. The fact I've just eaten lunch probably didn't help.

 

[AviatorInsight]

Here are some interesting videos of a BA flight going around at Gibraltar, reportedly due to wind.

The writer ponders at the end of the post whether this may be a pilot enduced manoeuvre to counter the wind.

Could this be the case?

If so, can you explain the physics of how/why is this effective?

INSANE Video Of British Airways Plane Approaching Gibraltar In Heavy Winds - One Mile at a Time

Far out! That definitely looked like PIO to me! The fact that it stopped so suddenly, gives me a clue that this may have been the case. Not sure what the Airbus autopilot is like maybe JB can help here but can you just throw the aircraft at the autopilot and it’ll engage? (not a good idea by the way).

The 737 needs to be in trim and no force on the control column to engage the autopilot.

In answer to your question, it’s never effective. Pilots usually get PIO in the simulator. You need to remember it’s a computer and doesn’t fly ‘exactly’ like the real thing but close to it. It only knows 0s and 1s. So early on in my training I learnt very quickly that if this were to happen in real life just let go of the controls for a second, let it settle and then keep it flying.

 

[jb747]

Far out! That definitely looked like PIO to me! The fact that it stopped so suddenly, gives me a clue that this may have been the case. Not sure what the Airbus autopilot is like maybe JB can help here but can you just throw the aircraft at the autopilot and it’ll engage? (not a good idea by the way).

The autopilot is never a cure. Just let go. The problem is that the control inputs are out of phase with the required motion. As soon as there's no input for a couple of seconds, the problem will be gone.

Airbus...again just let go, and the flight control system will then keep the aircraft where it happened to be at the time.

 

[747sp]

I was wondering if the separation rules were different between the Concorde and other planes when compared to normal takeoff and landings of heavy and small planes?
JB back in the day did you ever fly supersonic and does the same plane behave differently below the speed of sound when compared to flying faster than sound?

 

[jb747]

I was wondering if the separation rules were different between the Concorde and other planes when compared to normal takeoff and landings of heavy and small planes?

I don’t recall anything specific to Concorde, and as I only operated heavies near it, I wasn’t concerned about its wake. As its wing produced very strong vortices, it was probably categorised as a heavy, even though it wasn’t really....rather like the 757 is in a heavier category than its weight would imply.

JB back in the day did you ever fly supersonic and does the same plane behave differently below the speed of sound when compared to flying faster than sound?

You could get an A4 supersonic, but you had to mean it. I forget the profile, but it would have been in the order of 15-20º nose low, at full power, in the mid 20s. The limit was 1.2 mach, and I’m told that they went there easily until the refuelling probe was modified to the ‘bent’ shape from its original straight design. I managed 1.1 or so.

Aircraft behave very differently in the supersonic, transonic and supersonic regions. Basically the coefficient of lift is steady up until about .9, then it rapidly drops to about a third of its previous value, recovering somewhat on the supersonic side. That can lead to some nasty behaviour called ‘transonic tuck’ or mach tuck. Mach tuck - Wikipedia

The sort of behaviour you might see....if something like a Mirage starts max g turn at about 1.2 mach, the aircraft will have much more drag and will decelerate. As it slows into the transonic region, the coefficient of lift reduces, and more aft stick will be required to keep that same g. Then, as it slows further, the CL rapidly rises back to its normal subsonic level, and the g load will rapidly increase without any pilot input. Many a Mirage was overstressed this way.

Transonic is not a place to be. The .9 to 1.1 region is a place to pass through, not to stay.

 

[flyer89]

There’s a 2 part series on Concorde floating around on FOXTEL at the moment (BBC Knowledge?). I highly recommend it, what a remarkable machine.

 

[odysseus]

I was wondering if the separation rules were different between the Concorde and other planes when compared to normal takeoff and landings of heavy and small planes?
JB back in the day did you ever fly supersonic and does the same plane behave differently below the speed of sound when compared to flying faster than sound?

Some information on Concorde being classed as a heavy, reason and implications: Is Concorde Labeled As "Heavy"? - Airliners.net

 

[Quickstatus]

How much more flight time is added to QF1 SIN-LHR with the closure of Pakistani commercial airspace?

 

[defurax]

How much more flight time is added to QF1 SIN-LHR with the closure of Pakistani commercial airspace?

QF1 on 18th January almost completely avoided Pakistan, seems to add about 15 minutes or less...but I'll let the experts comment, just wanted to provide a data point.

 

[jb747]

QF1 on 18th January almost completely avoided Pakistan, seems to add about 15 minutes or less...but I'll let the experts comment, just wanted to provide a data point.

Probably not a great deal from the extra distance, but if everyone who normally routes over Pakistan is going down over Iran, those routes will become overcrowded, and then you may end up with aircraft going over Saudi and into Egypt. Loss of available altitudes will also have a negative effect.

The 380 (1 & 2) have enough available weight to carry quite a bit of extra fuel, and apart from extra time should not have too many issues. The 9 on the other hand, might be more affected. Not by the routing, as it tends to go quite a bit south anyway, but by extra traffic on those routes blocking its preferred altitudes.

 

[jb747]

Interestingly, I see that SQ have dropped a 380 into Dubai. I wonder how much of that was slot driven, as, from memory, the aircraft have about 15 tonnes of available weight. It may be that the SQ aircraft are operating to a lower MTW than the QF ones, but I wouldn’t have expected it to be more than about 5 tonnes.

Ah, just looked at the TAF for London, and it includes fog. Now that make sense...

 

[Quickstatus]

Interestingly, I see that SQ have dropped a 380 into Dubai. I wonder how much of that was slot driven, as, from memory, the aircraft have about 15 tonnes of available weight. It may be that the SQ aircraft are operating to a lower MTW than the QF ones, but I wouldn’t have expected it to be more than about 5 tonnes.

Ah, just looked at the TAF for London, and it includes fog. Now that make sense...

I recall the SQ Trent900 has a lower thrust rating maybe 2000lbs each x4 = 8000lbs less than QF. How much MTW does this reduce by?

Also, is there more fog in Spring?

 

[jb747]

I recall the SQ Trent900 has a lower thrust rating maybe 2000lbs each x4 = 8000lbs less than QF. How much MTW does this reduce by?

In itself there's no direct relationship. The aircraft would need to make certified climb gradients with an engine out, but the engine out performance was good enough that you normally didn't need to push the power up at all from the derated take off setting, even at max weight.

A more pertinent question would relate to the take off weights that SQ have purchased. When you buy an aircraft, everything is an option, and the right to use any given take off weight, even though there is no physical difference between aircraft, is something that the maker wants to be paid for. The QF aircraft, at their original 569 tonne MTW were heavier than many of the other operators....and at the end of last year, QF paid to have that limit increased to 572 tonnes. In that case, different nose gear tyres were fitted.

Also, is there more fog in Spring?

Don't know offhand, but my memory of fog in London was that it was always the freezing kind, so I think I mostly ran into it in winter.

 

[Quickstatus]

Did QF use all of the 572 tonnes?

 

[jb747]

Did QF use all of the 572 tonnes?

The increase to 572 only happened around January, and I never flew a flight that needed it in my remaining time. I would expect that it's used on most days for the 8 and the 94.

 

[Quickstatus]

So the engine thrust rating is a consequence of the required MTW rather than the other way round.

 

[jb747]

So the engine thrust rating is a consequence of the required MTW rather than the other way round.

Basically. But think engine out...as that will set the real limits.

 

[Fergo747]

When you buy an aircraft, everything is an option, and the right to use any given take off weight, even though there is no physical difference between aircraft, is something that the maker wants to be paid for.

You mention no physical difference but in the case of QF there was a need to fit a different nose gear to increase MTW. Are there any other modifications that would be made to increase the MTW or is it that the makers want to be paid more to 'certify' that, in this case, QFs A380s have a higher MTW than SQ?

Following on from this, does the certified (not sure if that's the correct term) MTW then pass in the event that QF sell or lease the aircraft to another operator (e.g. does VH-OQA retain it's MTW when it's sold)?

 

[jb747]

You mention no physical difference but in the case of QF there was a need to fit a different nose gear to increase MTW. Are there any other modifications that would be made to increase the MTW or is it that the makers want to be paid more to 'certify' that, in this case, QFs A380s have a higher MTW than SQ?

In many cases there is no difference whatsoever. A different nose gear tyre is very trivial, and you and I could have performed that mod given a set of instructions and a few hours (days, weeks). The various aviation authorities, and airports, etc, have habit of billing based upon maximum take off weight...irrespective of the weight that an aircraft actually operates at. That makes it very expensive to have addition weight that you don't use. For that reason, the QF 767s had their maximum reduced by about 20 tonnes when they ceased international operations. And even before that, there was a pair of weights that could be used (differing by about 13 tonnes), and the only difference was the plaque that engineering installed in the coughpit.

I don't think SQ has ever used their aircraft on ops that are quite as long as QFs Pacific flights, so they simply haven't needed extra. I expect that they could have increased the weight if they'd needed to.

Following on from this, does the certified (not sure if that's the correct term) MTW then pass in the event that QF sell or lease the aircraft to another operator (e.g. does VH-OQA retain it's MTW when it's sold)?

Good question, to which I can't provide an answer.