Lining up on the runway

[praa]

I hope some can give the answer to a question I've been curious about for a long time.
Although taxiways frequently meet a runaway at a gentle angle, some pilots prefer to enter at a more 'squared' approach and then align their aircraft on the centreline for take-off with a much sharper turn. It might gain about 10 or 20 yards but does that really matter? It happened last week at Heathrow on BA but I've also experienced it often at Munich (LH shorthaul) where the runways are long enough for any aircraft. Any ideas?

[Leezyjet]

The 3 most useless things in aviation :-

1) Runway behind you
2) Fuel in the bowser
3) Altitude above you

Normally taught from day 1 of training !!.

:}

[deltahotel]

If I'm cleared to take off as/before i enter, I'll probably do the gentle turn thing to get the power on and keep the ac moving. if I have to wait, i'll prob do the square off thing. does that help?

[Maude Charlee]

Also helps both pilots get a clear view of the approach to the runway to ensure that it is actually clear. Take nothing for granted.

[Flap 5]

Logically if you keep going from the taxiway you already have the taxi speed to benefit your takeoff roll. There is also the ATC clearance of 'cleared immediate takeoff' which would encourage this.

However there are a couple of reasons why a pilot may not do so.

1. The ATC clearance 'line up and wait' would preclude it.

2. Before setting take of thrust you 'stand up' the throttles / thrust levers to ensure both engines spool up - gas turbines are notorious at being slow to spool up. Then you increase the thrust to takeoff thrust. This ensures both engines increase to take off thrust at the same time. Doing this after a sharp turn on to the runway ensures you are not taxiing down the runway while the engines spool up (runway behind you being one of the useless items).

[frontlefthamster]

The 'gently angled' ones are Rapid Exit Taxiways, intended to allow aircraft to leave the runway at speed (typically 60 knots) after landing, thus reducing the time the aircraft occupies the runway.

The yelllow lines painted on the runway are, again, for vacating. When lining up, it is correct to maximise the runway length ahead.

[dogcharlietree]

It might gain about 10 or 20 yards but does that really matter?
For instance, years ago when DC-9's were operating RWY 08 at Essendon (Melbourne, Victoria) when weight limited, they would enter the runway, backtrack about 50 yards, then do a 180 degree turn to line up for takeoff. When doing the 180, the nosegear came within just a few feet of the end of the runway. The 180 was completed to the lined up position and the aircraft not allowed to roll forward. Every yard was needed. You don't need runway behind you when operating to the limits.

[deltahotel]

On a hot uphill runway in Arizona, We opened the C130 ramp to see to reverse so that the wheels were right on the beginning of the paved surface. Mr Boeing's majestic overpowering of ac combined with relatively light weights of freight make it less critical.

[praa]

Thanks for all the interesting answers folks but I'm still kind of curious about why for example an A319 pilot on a short-haul route out of Munich with a 4000m runway bothers to do it...

[Chesty Morgan]

He'd be ever so slightly miffed if he ran off the end of the runway by 10 or 20 yards! Even if it is 4000 meters long.

The 3 most useless things in aviation :-

1) Runway behind you
2) Fuel in the bowser
3) Altitude above you

Normally taught from day 1 of training !!.

Plus half a second ago.

[UniFoxOs]

Thanks for all the interesting answers folks but I'm still kind of curious about why for example an A319 pilot on a short-haul route out of Munich with a 4000m runway bothers to do it...

Don't forget the possibility of an aborted take-off - depending on the reason the pilot might not want (or be able) to brake all that hard - every extra yard of runway is worth having.

UFO

[Final 3 Greens]

Talking of linin gup on the runway, I took a flight on an A320 last night and the line up was not aligned with the runway direction. (ie noticeably crabbed)

During the low power pause, the aircraft was duly aligned with the centre line, but it struck me as being a bit scruffy and not up to the usual standard of ATPLs.

COmments welcome.

[Mshamba]

The length does not matter alone. Your takeoff performance is calculated for each takeoff with all those thousands of conditions to be considered. Apart from the runway length weight, temperature, QNH, wet/dry and so on. Normally your calculations "derate" your power. Therefore on long runways you do not takeoff with full power, you feed your FMC with the "power needed". Simply said: the longer the runway the less power your engines will produce. Conclusion: Even if the runway is 4000 m you will need 4000 m then as your performance is calculated for 4000 m and not for 3900 m if you would waste 100 m by a "smoother line up".

Thats just to be added to the reasons already stated above.

But i agree - 4000 m is more than sufficient. When i calculate the takeoff performance i usually calculate with a shorter runway by taken into account an intersection takeoff. If i need it - i am prepared. If i line up at the very end i have some reserves. But this is my opinion, ask 5 pilots and you get 10 different opinions.

[Pugilistic Animus]

The 3 most useless things in aviation :-

1) Runway behind you
2) Fuel in the bowser
3) Altitude above you

Normally taught from day 1 of training !!.
Except when you're on fire:}

edited to add: I've seen 'line up distance arguments'- between performance engineers here on Pprune that can make you a bit {fet}:\:}

[Flap 5]

Mshamba's reasoning also applies to intersection takeoffs. Even though you could well takeoff from an intersection with a long runway you do not do so because you often don't have the performance calculation for the intersection but only for the full length. Therefore you have to use the full length to remain safe and legal.