Starting takeoff roll

[Groundbased]

As an interested pax I was wondering what are the criteria that detemine whether you start the takeoff roll immediately on entering the runway or whether you stop after lining up.

I used to have an impression that it was necessary to stop and spool up a bit to ensure balanced thrust and then apply takeoff thrust, but maybe this is unnecessary or out of date today?

I also wondered if it may depend on the separation of incoming aircraft using the same runway, or the ATC clearance you receive. Possibly certain airports/runways have specific requirements? on a recent trip to Brazil it was apparent that the departure from Santos Dumont in Rio required a lot of powering up on the brakes before starting to roll.

Many thanks in advance for any replies

[VFE]

Good question. Often wondered myself, especially after being on board a 747-400 last year and the crew were razzing up the throttles before we were even lined up straight! :eek:
I would imagine it's down to ATC clearance, pilot preference and time/money saving factors - ie; they don't wanna take any longer getting up than they really need.

Sure someone here can say for sure.

VFE.

[Doors to Automatic]

I'd guess that stopping occurs if there is an aircraft ahead on the runway that has yet to vacate (i.e one that's just landed) or about to cross on an intersecting runway or taxiway.

At Santos Dumont the standing on brakes is due to a very short runway length

[Leslie]

It really does depend on the situation. If all the checks are complete with the cabin secure and crew strapped in, you are good to go. So if ATC clear you for departure before you reach the runway then if we are both happy, I wang it round the corner, spooling up the engines. The Thrust levers are moved forward about three inches and we look for about 1.2 EPR - You can note any slow acceleration from either pod and the engines respond much better from this setting rather than idle - thrust rate of increase is exponential.
I can call 'set power' just as we are straight. Of course the engines stabilise at 1.2 EPR which is alot of power so in slippery conditions care is required.
If this can be achieved it saves on brakes/wear and the engines actually prefer it (particularly with a proper crosswind) as they are getting a good flow of air. Older engines, I understand, could suffer from surge unless a rolling start was made in certain conditions.
The RR RB211's though are as good as gold - real beauties!
If the clearance is line up only then one quickly gets into position and waits for a take-off clearance so you can swiftly be on your way.
In certain icing conditions it is necessary to spool up the engines on the brakes so ensure any blade ice is shed. Power is the set after 10 seconds.
Holding her on the brakes and setting power as you release the brakes is great as a light 757-E4 at max chat nods and then screams off down the runway like a scalded cat - terrific fun and reassuringly powerful!
Hope this is clear enough an explanation as I have tried not to ramble too much!!!
Yours aye,
Leslie