737 Lining up- Question for DJ and QF crew
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Keg...
answering original question...
VB capts were told specifically that even the sharp 90 deg turn on to rwy is not necessary. That was a while ago, maybe some need to be retold.
Or have it in writing.
answering original question...
VB capts were told specifically that even the sharp 90 deg turn on to rwy is not necessary. That was a while ago, maybe some need to be retold.
Or have it in writing.
Surely it's all down to simple airmanship and courtesy to fellow aviators? If there's an aircraft on final right up your clacker and you are cleared 'immediate' why not gun it as you come around the corner and use the momentum to take care of any lack of line-up allowance? On the other hand, if it's a 'line up and wait' deal, why not use the extra few seconds available to optimise the take-off from a standing start and do a little turn away from the take-off direction (not a backtrack!) to be in position dead abeam the taxiway. Tyre wear shouldn't be that much of a consideration if the turns are done with some forethought.
If a 'heavy' goes off just ahead of me and I have to kill two or three minutes, I often then opt for the full backtrack to use the time, even though the numbers were crunched for the intersection. If is not holding anyone else up, of course. Sod's law says the time I could have done that, and didn't, will be the time one eats birds approaching V1.
If a 'heavy' goes off just ahead of me and I have to kill two or three minutes, I often then opt for the full backtrack to use the time, even though the numbers were crunched for the intersection. If is not holding anyone else up, of course. Sod's law says the time I could have done that, and didn't, will be the time one eats birds approaching V1.
Line Up Allowances for VB 737 (90 degree turn/180 degree turn)
700 22.5/29.0 (ASDA) 9.9/16.4 (TORA)
800 26.4/35.2 (ASDA) 10.8/19.2 (TORA)
As its ATC's runway any backtrack would be subject to their approval but I will s-a-s use as much of the available runway that I legally can.
"Mini back tracks" are in the eye of the beholder though!
- can't say I use em.
700 22.5/29.0 (ASDA) 9.9/16.4 (TORA)
800 26.4/35.2 (ASDA) 10.8/19.2 (TORA)
As its ATC's runway any backtrack would be subject to their approval but I will s-a-s use as much of the available runway that I legally can.
"Mini back tracks" are in the eye of the beholder though!
- can't say I use em.
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Are they asking ATC for a back-track?
I once back-tracked all of about 5-10 metres at Essendon when I slightly overshot the taxiway. I was STERNLY spoken to by ATC about requiring permission to back-track. I replied with "yeah, whatever mate." I was the only aircraft within 5 miles.
You need to be careful when accepting intersexual departures when offered. I was once happy to accept one at Albury and when I lined up was asked if I was happy to accept a 7-8 knot tailwind. Whilst I accepted because I had power and climb to burn, if it had been a low time hour-building pilot in a 172 with his cost-sharing high-school mates on-board it would have been a different story.
I once back-tracked all of about 5-10 metres at Essendon when I slightly overshot the taxiway. I was STERNLY spoken to by ATC about requiring permission to back-track. I replied with "yeah, whatever mate." I was the only aircraft within 5 miles.
You need to be careful when accepting intersexual departures when offered. I was once happy to accept one at Albury and when I lined up was asked if I was happy to accept a 7-8 knot tailwind. Whilst I accepted because I had power and climb to burn, if it had been a low time hour-building pilot in a 172 with his cost-sharing high-school mates on-board it would have been a different story.
Bottums Up
The original question.
An answer.
An opinion:
I can't see that a mini back track, followed by a turn of > 110 degrees can reduce tyre wear or undercarriage stresses, compared to a 90 degree turn.
they mostly go for a 'mini back track'. IE if cleared to line up at 34 Juliet in MEL, rather than taxi out and do a 90 degree right turn to align with the center line, they follow the lead in line to the south before lining up with a 110 degree (or more) turn to the north to line up.
I think to reduce tyre were and stresses the most correct.
I can't see that a mini back track, followed by a turn of > 110 degrees can reduce tyre wear or undercarriage stresses, compared to a 90 degree turn.
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Bugger the mini backtrack, there's plenty of margin in the takeoff calcs, gently line it up without scrubbing the tyres but dont use more than the lineup allowance.
Most jet aircraft using asummed temperature takeoff method include about 250 metres of pad.
Calculations with headwinds automatically factor in only 50% of that headwind actually being available, alternatively tailwinds are factored to 150%.
Maybe for large aircraft like the B744 or A380/A340 when conditions are limiting, otherwise it sounds like the 737 boys are lining up like the long wheel base big boys do.
MC
Most jet aircraft using asummed temperature takeoff method include about 250 metres of pad.
Calculations with headwinds automatically factor in only 50% of that headwind actually being available, alternatively tailwinds are factored to 150%.
Maybe for large aircraft like the B744 or A380/A340 when conditions are limiting, otherwise it sounds like the 737 boys are lining up like the long wheel base big boys do.
MC
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Maybe for large aircraft like the B744 or A380/A340 when conditions are limiting, otherwise it sounds like the 737 boys are lining up like the long wheel base big boys do.
bbbbbbbzzzzzzzzzzzzzbbbbbbbbbbbzzzzzzzzzzzzzzzz
In this day and age of litigation, I reckon if the mini-backtrack thingy was required or even a good idea, then it would be recommended by Boeing and also by the Qantas and Virgin training departments.
As this does not appear to be the case, and also considering the increased stresses on the nose gear and the common courtesy aspects, there would appear to be very little to recommend it and indeed much to make it seem the least attractive of the alternatives.
That's my 2 cents worth, take it or leave it, but I shall continue to laugh at those that persist with this foolhardiness.
And if things are that bloody tight, then for Gods sake at least
use the full length!
As this does not appear to be the case, and also considering the increased stresses on the nose gear and the common courtesy aspects, there would appear to be very little to recommend it and indeed much to make it seem the least attractive of the alternatives.
That's my 2 cents worth, take it or leave it, but I shall continue to laugh at those that persist with this foolhardiness.
And if things are that bloody tight, then for Gods sake at least
use the full length!
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Following on from your reasoning. If there is "plenty of margin in takeoff calcs" what should it matter if it is a 737 or an A380 stretch at MTOW?
why not gun it as you come around the corner and use the momentum to take care of any lack of line-up allowance?
Luckily we hadn't gunned it as we came around the corner.
todays reading is from FCT737NG(TM) revision number:7, page 2.8, October 31,2007.
turns of 90 degrees or more
initiate the turn as the intersecting taxiway centerline (or intended exit point) approaches approximately the center of the number 3 window. Initially use approximately full nose wheel steering wheel displacement. Adjust the steering wheel input as the airplane turns to keep the nose wheels outside of the taxiway centerline, near the outside radius of the turn. Nearing turn completion, when the main gear are clear of the inside radius, gradually release the steering wheel input as the airplane lines up with the intersecting taxiway centerline or intended taxi path.
Now may God help anyone who does anything else but this, I dont know how they sleep at night
.
hoss
ps. Keg, unfortunately I cannot answer your question and have spent many times wondering why some airmen do this as well. its not my thing but like many things in aviation if i put my mind/experience to it i can usually find three good points and at the same time three bad points to almost anything. i'm sure they have a valid reasoning for their technique. who knows maybe in a few years or even next week you may find yourself doing this technique with a strong view for it.
turns of 90 degrees or more
initiate the turn as the intersecting taxiway centerline (or intended exit point) approaches approximately the center of the number 3 window. Initially use approximately full nose wheel steering wheel displacement. Adjust the steering wheel input as the airplane turns to keep the nose wheels outside of the taxiway centerline, near the outside radius of the turn. Nearing turn completion, when the main gear are clear of the inside radius, gradually release the steering wheel input as the airplane lines up with the intersecting taxiway centerline or intended taxi path.
Now may God help anyone who does anything else but this, I dont know how they sleep at night
.hoss
ps. Keg, unfortunately I cannot answer your question and have spent many times wondering why some airmen do this as well. its not my thing but like many things in aviation if i put my mind/experience to it i can usually find three good points and at the same time three bad points to almost anything. i'm sure they have a valid reasoning for their technique. who knows maybe in a few years or even next week you may find yourself doing this technique with a strong view for it.
Last edited by hoss; 26th Nov 2008 at 12:36.
Nunc est bibendum
Thread Starter
Maybe for large aircraft like the B744 or A380/A340 when conditions are limiting...
Keg,
That's longer than my whole aeroplane!
esreverlluf
The only legal requirement is that you line up within the lineup allowance. In some aircraft, that requires a near pirouette on the inboard tyres (My dad used to do them in DC-3s - but they had a big shiny round steel plate to do it on to help). Have close look at a set of tyres doing such a manoeuvre. To give yourself even more of a surprise, watch a two-axle bogey during a really tight turn.
A bit of a wider turn to line up with a micro "backtrack" is good sense to me. If you don't have to, what's the point subjecting the structure to unnecessary wear? You might find later on it does a QF Rome gear collapse...
A380 Driver,
No, I am not. But the Ops Manual says that you must line up within the lineup allowance, so that's what pilots do. Sounds fair to me.
I suggested an alternative but was ignored. Yes, it would be nice to apply commonsense to aviation sometimes, but, particulary in this day and age, why bother setting yourself up for a punch in the nose?
That's longer than my whole aeroplane!
esreverlluf
In this day and age of litigation, I reckon if the mini-backtrack thingy was required or even a good idea, then it would be recommended by Boeing and also by the Qantas and Virgin training departments.
A bit of a wider turn to line up with a micro "backtrack" is good sense to me. If you don't have to, what's the point subjecting the structure to unnecessary wear? You might find later on it does a QF Rome gear collapse...
A380 Driver,
Bloggs- Surely you are not suggesting that the figures you use for 21 takeoff (full length) are in anyway limiting even at a full flex at Max TOW.
If you feel the 90deg is allowance is not enough then push them to change it.