The answer to all our secrets

[Nicholas49]

Rushed take-off?

I want to open a thread about something I've noticed on the last few short-haul flights I've taken. I'm not sure if this is an issue or not (I'm sure I'll soon be told if it isn't!).

I've noticed that some pilots on short-haul flights "rev" (sorry - don't know the technical term) the engines to check they're stable literally as they are still turning onto the runway and before they are lined up.

Is this a common and accepted practice? Do any professional pilots frown upon it? (For example, if it caused you to mess up your alignment.) Is it at all a sympton of a rushed take-off?

I'd appreciate your comments.

[chiglet]

I've been on the Flight Deck, and on approaching the Holding Point, have heard XXX123 are you ready Immediate?. If yes, then a/c is cleared for an "Immediate Take Off". A/c "spools up the engines" [advances the throttles] and enters the Runway...and departs.
IF not ready, then hold until they are.
Also in 35 years of [Civil] Aviation, I've lost count of the number of "rushed" departures
watp,iktch

[Caudillo]

Nothing to do with being rushed. It's a "rolling takeoff" - happens when all preflight checks are completed, the cabin is secure, and clearance to take off has already been given prior to entering the runway or whilst entering it. Of course you check with the guy in the seat next to you that he is happy to continue and off you go. Useful to keep the flow up on a busy strip.

[BYALPHAINDIA]

I Think we have seen more 'rushed' T/Offs since the low cost has boomed, I can't remember the last time I saw an Aircraft doing an 'on the brakes roll off'

I still miss the DC9'S at the end of LBA'S R14, Doing a full thrust roll off the brakes!!

I remember an FR 737-200 in a rush going off R14 years ago, He was in a rush and had to be told to wait!!

The tower said wait, And he replied I can't wait!!

[Bullethead]

G'day Nicholas,

The reason sometimes that jet aircraft are stopped on the runway and part power is applied before takeoff thrust is set is because sometimes the engines initially accelerate unevenly from idle. So rather than setting takeoff thrust straight from idle and getting a large thrust imbalance, part power is set, the engines stabilised and then takeoff thrust is set.

When doing a rolling takeoff you can advance the throttles as you enter the runway and if it all looks good then you can set takeoff thrust without getting a thrust imbalance.

It's not a rushed takeoff but an expedient way of entering the runway and taking off without stopping.

I'd be surprised if any jet operators set takeoff thrust on the brakes.

Regards,
BH.

Hey Mods, Has this thread been merged with another one?

[Rainboe]

Answer removed as question is rude!

Hopefully thread ended- I find the manner of querying it slightly offensive- it was more a burrowing exercise than an outright question. Where ever did 'rushed'/'messing up alignment' come into it?

[Nicholas49]

Rainboe:

I raised the question because I wanted to know the answer, not because I was "burrowing". What a ridiculous assumption. If you check the name on the forum, you'll see that it's designed for questions. If you don't want to answer questions, then don't.

Bullethead, Caudillo and chiglet:

Thank you very much guys for your helpful, informative explanations.

[ChristiaanJ]

On Concorde, you couldn't even do a "run-up on the brakes"... the aircraft would have literally started sliding forward.
So you lined up, did your last checks, released the brakes and slammed the trhottles forward, then very carefully monitored spool-up, reheat lighting correctly, etc., during the first few seconds of the take-off roll.

[Rainboe]

Nicholas49, I did take the trouble to answer your question, so i assume you were still thankful to me for doing so, even though I disliked your reference to
<<Is it at all a sympton of a rushed take-off?>>....an offensive comment you did not need to add. You could have simply asked the question without trying to burrow and discover what you thought may be a defective operation!

I have now removed my answer.

[Nicholas49]

Rainboe,

I was of course grateful for your taking the time to answer the question.

I asked whether the practice was the symptom of a rushed take-off because it can appear that way to passengers. I remember when aircraft always waited on the runway before taking-off.

To clarify: by "rushed" I did not mean to imply inept piloting. Instead, I thought this practice may have been the take-off equivalent to the intensive-braking used to vacate a runway quickly when aircraft are waiting to land.

It is clear from everyone's answers that the practice is standard.

It was certainly not intended to be offensive.

[Rainboe]

I understand. No aircraft need wait on the runway- pre-takeoff checks can be rapidly completed. The only reason there is a pause before take-off is to wait for a preceding aeroplane to take-off and get clear, or one to land and clear before brakes release. Powering up on brakes is not desired or recommended, though an intermediate power may be required in icing conditions to ensure the engine de-icing can work long enough to ensure there are no problems during high power for take-off. So the ideal is to turn onto the runway and keep it rolling while you spool up the engines, without touching the brakes.

[clifftop]

Having watched hundreds of aircraft take off from LPL whilst listening to comms from tower - pilot, It is a fairly regular thing to hear the pilot say "ready on reaching" as he approaches the holding point short of the rwy.
I have also heard the ATCO ask the pilot "are you ready for immediate departure?" this is often when there are aircraft on finals to get the departure off the ground sooner rather than later.

I am aware that LPL is under certain jurisdiction from Manch, there is usually a delay between each IFR departure as dictated by Manch.

[Nicholas49]

Thanks, Rainboe.

[magpienja]

Question regards braking on landing.

Hi guys I was watching some landings a Liverpool this morning runway wet, a 737 and a airbus think it was a 320 landed while I was there, on touch down with both aircraft I could hear a screeching noise sounded like tyres skidding for quite a few seconds after touchdown,

Would that be what I could hear, if so do the brakes come on automatically.

Nick.

[BOAC]

Just the anguished sound of rubber accelerating from standstill to touchdown speed. 'Braking' in reverse if you like.

[FlightDetent]

Originally Posted by clifftop

ATCO ask the pilot "are you ready for immediate departure?"

Perhaps it may be intresting to know that "immediate departure" is in fact an estabilished code phrase used to describe rolling take-off Rainobe and Nicholas have been discussing so eagerly.

[clifftop]

That's why I posted the reply.

[NW1]

For supersonic acceleration (Mach 1 to about Mach 1.7), Concorde needed all four reheats (too much asymmetric thrust with three).

If one didn't light you could still do the accel. If two failed it was unlikely to work - what dictated whether it worked was not the number of reheats but getting to M1.7 by the 15' accel limit on reheat use - there was no problem with assymetrics. Actually somedays (e.g. cold OATs) the accel could outpace the fuel transfer, the technique then was to switch off one reheat to allow the fuel to catch up...

So if for whatever reason one of the reheats didn't light at the start of the take-off roll (which occasionally did happen), the take-off was abandoned, and the aircraft would return to the stand.

Again, not quite right. It was a matter of performance - if the TOW was a certain margin below PLTOW (using a graph in the performance manual) then you only needed 3 reheats (called a "GO" takeoff), otherwise you did need all four (called a "STOP" takeoff). This check was made at 100kts not 60kts - the NHP called "100kts" and if all was well the E/O called "power set" and off you went. Interestingly, a single reheat failure after 100kts did not constitute an engine failure and you carried on irrespective of TOW (rare: once lit they tended to stay lit - it was getting them lit that could be problematic....). Two reheats out constituted an engine failure and was treated in the conventional way...

Such a rejected take-off was a pretty straightforward affair, because the aircraft would usually not have reached more than about 50mph

See above - the reheat GO/NO-GO decision was made at 100kts.
Offered purely out of interest - hope it helps...

[ChristiaanJ]

NW1,
Many thanks!
And apologies to all for providing less than exact info.
CJ

[NW1]

...you're welcome - don't apologise; it's only a chat!