737 Lining up- Question for DJ and QF crew
Nunc est bibendum
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737 Lining up- Question for DJ and QF crew
Got a question that is mostly directed towards the DJ 737 crew although it does also apply to a few of the QF 737 mob also.
On the few occasions where I taxi out behind a DJ 737 (mostly we're in front
) I've noticed that when the DJ 737 is cleared to line up (and often when cleared for take off also) 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've seen the same thing in at MEL 27, SYD 16R Foxtrot and even 16R B2! 
To ensure that this isn't seen as a DJ bashing exercise I've seen a few of our guys do it as well.
When seeing it I've always thought that if you were that desperate for runway length then surely full length would be a better option. I admit that perhaps I've missed something so I have a number of questions relating to this that tend to flow on from each other.
I'm familiar with the old axiom about 'runway behind', etc. We can leave that behind because that's only one aspect of being a professional aviator. Besides, if that were the case then we'd all be taking off from A, B1 or B2 on SYD 16R.
Another reason I ask (apart from idle curiosity) is that there have been a couple of times where this 'mini back track' has taken up enough extra time to ensure that the next aircraft in line (not always me) hasn't gotten away due to the preceding departing taking too long and the next arrival now too close. I've started the clock on a few occasions and from the line up clearance (or take off clearance) to a particular point on the runway on the take off roll (no delay on take off clearance) has taken significantly longer than someone who followed the lead in lines onto the runway and applied thrust along the way- up to 30 seconds. Even taking into account individual pilot nuances, in times of peak congestion this is a significant issue in utilising the runway environment effectively.
Anyone able to shed some light? PM if you like.
On the few occasions where I taxi out behind a DJ 737 (mostly we're in front
) I've noticed that when the DJ 737 is cleared to line up (and often when cleared for take off also) 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've seen the same thing in at MEL 27, SYD 16R Foxtrot and even 16R B2! To ensure that this isn't seen as a DJ bashing exercise I've seen a few of our guys do it as well.When seeing it I've always thought that if you were that desperate for runway length then surely full length would be a better option. I admit that perhaps I've missed something so I have a number of questions relating to this that tend to flow on from each other.
- Is it simply about not wasting the runway?
- If so, is the 30m saved that critical?
- If the 30m isn't that critical and you're using it simply to increase your margin then in the event of a subsequent incident is a lawyer is going to have a field day and say that if you felt that the extra distance was warranted then why not go to full length?
- I presume you're de-rating in which case why not just reduce the de-rate?
I'm familiar with the old axiom about 'runway behind', etc. We can leave that behind because that's only one aspect of being a professional aviator. Besides, if that were the case then we'd all be taking off from A, B1 or B2 on SYD 16R.
Another reason I ask (apart from idle curiosity) is that there have been a couple of times where this 'mini back track' has taken up enough extra time to ensure that the next aircraft in line (not always me) hasn't gotten away due to the preceding departing taking too long and the next arrival now too close. I've started the clock on a few occasions and from the line up clearance (or take off clearance) to a particular point on the runway on the take off roll (no delay on take off clearance) has taken significantly longer than someone who followed the lead in lines onto the runway and applied thrust along the way- up to 30 seconds. Even taking into account individual pilot nuances, in times of peak congestion this is a significant issue in utilising the runway environment effectively.
Anyone able to shed some light? PM if you like.
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I presume you're de-rating in which case why not just reduce the de-rate?
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Gidday Keg,
my own observation has been that "mini backtracks" usually take place when there is time to spare.
ie. "QF878 line-up only, traffic to land runway 27 prior to your departure."
I suppose it's one of very few ways I can get a warm fuzzy feeling with a few wriggles of the wrist these days!
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my own observation has been that "mini backtracks" usually take place when there is time to spare.
ie. "QF878 line-up only, traffic to land runway 27 prior to your departure."
I suppose it's one of very few ways I can get a warm fuzzy feeling with a few wriggles of the wrist these days!
bbbbbbbbbzzzzzzzzzzzzbbbbbbbbbzzzzzzzzzzzzzzzz
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Watched an airvan take off from Meekatharra month or so ago. Lined up mid field and hit the taps with 3 or 4 pax on board. Three of us stood there with our jaws dropping to the ground watching in amazement as he hurtled down the runway in a mad attempt to get airborne. He only just cleared the fence by inches. If only they knew how close they came to ending up in a big heap that day.
I do it and I'm certainly not flying anything the size of a 737. I was under the impression that the yellow taxi line was there to indicate the path for aircraft LEAVING the runway while those entering the runway should do so in a way to maximise the TORA.
Nunc est bibendum
Thread Starter
I was under the impression that the yellow taxi line was there to indicate the path for aircraft LEAVING the runway while those entering the runway should do so in a way to maximise the TORA.
Green Gorilla, doing a mini back track (turn to the left) and then a 120 degree turn on full lock back the other way is going to do a lot more to reduce the life of the tyres and gear than just doing a nicely rounded turn in the one direction.
Mr Buzzy may be close to the money although I have seen them at other times. He's probably also on the money as to the reasons why!
tinpis, classic!
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Ive seen an NJS 146 come within a bees dick of removing the thereshold lights at ph on runway 21 doing exactly this. I'd recommend a read AIP ENR 1.1 para 5.2.2 if you find yourself "using every inch" of runway. I find it quite amusing when such things happen only to observe the subject aircraft creep forward while holding lined up and waiting for clearance to take off.
Years ago I was jumpseating on an Ansett 767 outa BN on a A7 departure and infront a 737 did the exact thing you mentioned Keg.
This old Captain on the 767 turned around and said to me, look at this ******, as he said if I was that desporate for an extra 10 metres I wouldn't be stuffin around with the intersection!
I think there were also some negative comments about the 737 as well but that is not expected from 767 skipper is it ?
This old Captain on the 767 turned around and said to me, look at this ******, as he said if I was that desporate for an extra 10 metres I wouldn't be stuffin around with the intersection!
I think there were also some negative comments about the 737 as well but that is not expected from 767 skipper is it ?
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Try that trick at most busy overseas airports, especially Europe, and ATC will give you a right bollocking (and rightly so). The comments will be along the lines of 'you accepted intersection X, if you require backtrack you must advise so adequate spacing can be provided. This has been heard many times even for the slightest of backtracks.
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Back in my Darwin days, Air North were good at the mini-backtrack thing. We asked them about it and they said (IIRC) that it was a kind of company policy thing to make sure the TORA numbers were exactly right for the intersection departure. After asking a few more pilots it turned out that the figures took into account turning onto the runway directly from the intersection so the backtrack was pretty much unnecessary. It does make a difference, as Keg pointed out, when trying to run things as close as safely possible.
Cheers,
NFR.
Cheers,
NFR.
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It's just less than optimal airmanship fuelled by lack of understanding (although motives may be pure).
If you look at over-run accidents, I think you'd be hard pushed to find one instance where an extra 30 m would have mad a difference. It's the same as an approximate 0.4 second delay in abort decision at 150 kts.
As others have said, if you're that tight on tarmac, don't take an intersection - that's where airmanship comes in, not by trying to milk extra field out of an already accepted reduced length.
If you look at over-run accidents, I think you'd be hard pushed to find one instance where an extra 30 m would have mad a difference. It's the same as an approximate 0.4 second delay in abort decision at 150 kts.
As others have said, if you're that tight on tarmac, don't take an intersection - that's where airmanship comes in, not by trying to milk extra field out of an already accepted reduced length.
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Try that trick at most busy overseas airports, especially Europe, and ATC will give you a right bollocking (and rightly so). The comments will be along the lines of 'you accepted intersection X, if you require backtrack you must advise so adequate spacing can be provided. This has been heard many times even for the slightest of backtracks.
Dublin RWY 28 has a similar setup to what Keg describes..but ATC are aware of it, and thus compensate. I wonder if ATC at MEL have observed the lineup technique first-hand? and if so..are they shouting down the mic at the DJ crews?
The TORA quoted for an intersection departure is calculated from the intersection of the extended downwind edge of the relevant taxiway. So if you follow the TWY centre line out and line up you will always be short of the quoted TORA (admittedly not by much although if it is, say, a RWY 01 A6 departure at BNE it could be a couple of hundred metres or so because of the diagonal angle.)
Mind you this is no different to full length as once you line up the short part of the RWY underneath you and behind you is also part of the TORA you are working with.
Mind you this is no different to full length as once you line up the short part of the RWY underneath you and behind you is also part of the TORA you are working with.
Couldn't agree more Keg & well said Cloudcutter.
I have seen quite a lot of DJ and QF 737s doing the minibacktrack thing - do they not know that there is a line-up allowance (and quite a generous one) provided for in the performance charts?
I had come to the conclusion that it is just part of the general "shorthaul culture", probably for reasons that have been lost in antiquity.
However, I doubt if we'll see any difference as a result of posting here!
I have seen quite a lot of DJ and QF 737s doing the minibacktrack thing - do they not know that there is a line-up allowance (and quite a generous one) provided for in the performance charts?
I had come to the conclusion that it is just part of the general "shorthaul culture", probably for reasons that have been lost in antiquity.
However, I doubt if we'll see any difference as a result of posting here!
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I always have a chuckle when I see a mini backtrack, 30 metres at 130kts doesn’t take long.
From what I have seen QF and DJ both do mini backtracks at about the same rate.
Is this pprune or not, why hasn't Jetstar been dragged into it.
From what I have seen QF and DJ both do mini backtracks at about the same rate.
Is this pprune or not, why hasn't Jetstar been dragged into it.
The aircraft is required to be lined-up within the lineup allowance. The lineup allowance for our "Boeing" for a 90° turn on is very very tight, and hence for an intersection departure, many of us will "swing" towards the threshold a little to increase the radius of turn to the lined-up position and reduce stress on the gear and wear on the inboard tyres.
Quite frankly, runways with "indents", such as 21 at Perth (and 06 to a lesser extent - brand new taxiway too!), are a nuisance because, if one is to comply with the rules, one has to do a quite tight turn to still get lined-up within the lineup allowance.
One solution is to use an RTOW chart for an intersection further down the runway. Then you don't have to worry about the lineup allowance. You can do a nice wide rolling turn and off you go!
I can assure you that in the event of a mishap on takeoff, you will be asked why you did not line up within the lineup allowance. Perhaps DJ 737 drivers are just preventing that scenario. You can argue with the lawyers all you like "But sir, there was plenty of runway!" "Was there Bloggs?". They'll have your guts for garters nevertheless!
Keg, what's the 90° lineup allowance in your machine?
Quite frankly, runways with "indents", such as 21 at Perth (and 06 to a lesser extent - brand new taxiway too!
), are a nuisance because, if one is to comply with the rules, one has to do a quite tight turn to still get lined-up within the lineup allowance.One solution is to use an RTOW chart for an intersection further down the runway. Then you don't have to worry about the lineup allowance. You can do a nice wide rolling turn and off you go!
I can assure you that in the event of a mishap on takeoff, you will be asked why you did not line up within the lineup allowance. Perhaps DJ 737 drivers are just preventing that scenario. You can argue with the lawyers all you like "But sir, there was plenty of runway!" "Was there Bloggs?". They'll have your guts for garters nevertheless!
Keg, what's the 90° lineup allowance in your machine?
