737 Lining up- Question for DJ and QF crew

[Keg]

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 :E :} ) 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! :eek: 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.

[tinpis]

"Hey, thats Keg behind us isnt it?"

"Yup"

"Lets do that back track thingy and give him the sh!ts"

[DeltaT]

I presume you're de-rating in which case why not just reduce the de-rate?

At a guess, the reduction in the de-rate for take-off will burn more fuel than the fuel expended on the line up procedure you describe.

[Mr.Buzzy]

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!:ok:

bbbbbbbbbzzzzzzzzzzzzbbbbbbbbbzzzzzzzzzzzzzzzz

[ForkTailedDrKiller]

Tinny, let me guess! You moonlight writing stuff for Gary Larsen, huh?

Dr :8

[solowflyer]

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. :eek:

[Wing Root]

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.

[Capt Claret]

Green gorilla, two questions please.

What does <p> ..... </p> mean?
How does it reduce tyre wear?

[Hasselhof]

<p> is where he started to p, and </p> is where he finished p-ing. The reduced weight in fluid loss would probably work someway towards reducing the wear in mention.

[Keg]

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.

Sure, but when cleared 'line up, be ready immediate' the last thing I want to see is the bloke in front back tracking. Even if it's not a 'be ready immediate' you can still minimise runway occupancy (and wear and tear on the tyres and gear) by not doing a right angle turn but using a more gradual turn onto the runway. Even if someone doesn't follow the lead in/ lead off lines then they can still be a lot quicker than the mini-back track takes.

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! :ok:

tinpis, classic! :D :}

[Mystyler]

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.:D

[puff]

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 ? :)

[BalusKaptan]

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.

[No Further Requirements]

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.

[Cloud Cutter]

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.

[haughtney1]

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.

Fair enough BalusKaptan, although most modern European airports ie FRA, CDG, MAD, BCN, FCO, LGW, LHR, are designed with specific lead in guidance for when you enter the runway environment ala cat 2 or 3 complience..so in essence its not an issue.
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?

[Traffic_Is_Er_Was]

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.

[esreverlluf]

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! :ugh:

[toolish]

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.

[Capn Bloggs]

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!:ugh:), 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?

[Keg]

Bloggs, 28 metres.

Thanks all for the contributions. I appreciate it.

[Capt Fathom]

There was a answer to Kegs' question amongst all of that? I must pay more attention during class!

[Yusef Danet]

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.

[Green gorilla]

I think to reduce tyre were and stresses the most correct.

[Mach E Avelli]

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.

[ad-astra]

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.

[VH-XXX]

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.

[Capt Claret]

The original question. 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.

An answer.I think to reduce tyre were and stresses the most correct.

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.

[Buster Hyman]

Perhaps they require both crew to visually confirm that no one is about to land on them?

;)

[Mstr Caution]

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

[Pedota]

VH-XXX "You need to be careful when accepting intersexual departures when offered".

You certainly do!

[Mr.Buzzy]

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.

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?

bbbbbbbzzzzzzzzzzzzzbbbbbbbbbbbzzzzzzzzzzzzzzzz

[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.

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 :ok:use the full length!

[Mstr Caution]

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?


Last time I looked an A380 at MTOW is still alot longer in length than a 737 at MTOW.

[framer]

why not gun it as you come around the corner and use the momentum to take care of any lack of line-up allowance?
That would be fine if you, or your f/o, don't make the mistake I have seen made twice in the 737. That is to push the thrust levers right up to an aproximate take-off power setting in one swift movement. I have no idea why they did it, and in both cases neither did they, but they did it, and the thrust didn't come up evenly at all! :uhoh:

Luckily we hadn't gunned it as we came around the corner.:)

[hoss]

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.

[Keg]

Maybe for large aircraft like the B744 or A380/A340 when conditions are limiting...

I often took off at limit weights on the 744. Never once did I see someone try and grab a few extra meters. :}

[Mstr Caution]

Keg, Clarifying my statement.

Upto 90 degree turns if required in long wheel base aircraft, but not more than 90 degree turns required.

[Keg]

Ah, copy. Thought the original comment didn't read quite right.

[Capn Bloggs]

Keg,
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.

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,
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.
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.

If you feel the 90deg is allowance is not enough then push them to change it.
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?

[-438]

I have never quite understood the mini back track either.

Delta T, when you wrote,
"At a guess, the reduction in the de-rate for take-off will burn more fuel than the fuel expended on the line up procedure you describe."

I'm not sure if I've understood your double negatives correctly. But wouldn't max grunt take off use less fuel than a de-rated take off?

[greenslopes]

But what I really love is ATC wait till the landing aircraft has landed and vacated and the advise..."line up-be ready immediate".....................Why don't they give clearance to line up behind more often and the crew lining up would not feel so under the pump to get into the air.
If you line up behind the landing you can do your little backtrack and not set anyone's bloodpressure rising.

Just a thought

[No Further Requirements]

greenslopes

Sometimes tower controllers are hesitant to line up aircraft if the airspace they are firing you into is black with aircraft. It's not a nice feeling to line up someone behind the landing, with someone on final, and go to Approach for departure instructions to which they answer 'call you back'. There's a lot more going on up in the tower than you realise sometimes, and it's not just about the aircraft you can see and hear in the immediate vicinity.

Cheers,

NFR.

[DeltaT]

I'm not sure if I've understood your double negatives correctly. But wouldn't max grunt take off use less fuel than a de-rated take off?

If that were true, why don't planes fly around full throttle all the time?
(granted the exception of Concorde)

[Icarus2001]

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.

A bit of a wider turn to line up with a micro "backtrack" is good sense to me

Capn Bloggs Can I suggest that you take out a piece of paper and DRAW what you are suggesting, it makes no sense. A "mini back track" DOES NOT "increase the radius of turn". Nor is it WIDER! The greatest RADIUS of turn is gained by turning right or left 90 degrees on to the runway. By backtracking slightly you increase the degrees to be turned through in the same available width of runway so as Capt claret says...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. The MORE degrees you turn the aircraft through THE MORE the inside bogey slows down or stops, INCREASING tyre wear!

If you have an issue lining up inside the allowance on runway 21 at Perth then I suggest you need to get out more.:hmm:

By the way, does your company lineup procedure measure to the main wheels, nosewheel, pilot position or aircraft data plate back to the threshold?

[-438]

I am of the understanding that full rated take off and climb will use less fuel than de-rated takeoff and climb. The cruise is another story.
However I'm quite happy to be informed otherwise.
Any excuse not to de-rate.

[Capn Bloggs]

Icarus,

I suggest that you take out a piece of paper and DRAW what you are suggesting, it makes no sense.
As requested (inboard main wheel shown):

http://i521.photobucket.com/albums/w334/capnbloggs/lineup.jpg

By the way, does your company lineup procedure measure to the main wheels, nosewheel, pilot position or aircraft data plate back to the threshold?
I have no idea what you are talking about. Lineup allowance is lineup allowance. How it is practically applied is irrelevant. If you don't know how it is measured, I suggest you get into the certification rules.

[Keg]

Bloggs, nice piccie. I should note that your piccie is not what I was asking about in the first instance. I can't possibly replicate your drawing but what I've observed most often is the aircraft following the guidance until the nosewheel is on the runway then doing a sharp (20 degrees or so) turn in the opposite direction to the take off direction and then doing a sharp (full lock) 110 degrees turn back the other way. I agree that the drawing you illustrate would enable less tyre scrub but that ain't what most of these guys are doing.

[hongkongfooey]

I am of the understanding that full rated take off and climb will use less fuel than de-rated takeoff and climb.

True, de-rate is about reducing engine wear, not fuel consumption

[DeltaT]

Only because it takes longer to get to cruise height.