Full power with brakes on
 

I've flown many times but I took two flights recently that were unusual in terms of the take off.

Both flights were with Islandsflug on a 737-400.

Our take off started with the usual spooling up of the engines then full power so that you were pushed into the seat. However, brakes were still on and remained on for approx 5 secs. Then the brakes came off and it felt like we had been flung down the rwy on a catapult.

I enjoyed it as it was different but it seemed to bother a number of the passengers. One guy behind me turned to his wife and said "that will be the handbrake off then!"

What are the reasons why this would happen?

1st take off was at EGNT (so runway length not a problem) and the return at Zakynthos.

Many thanks.

dgutte - one minor correction, I think - you will not be 'pushed into your seat' UNTIL the brakes come off!

My guesses:

Normally, in winter where engine icing is more prevalent, this is a normal procedure. The engine is run up (737) to 70% of max RPM (NOT 'full power') for about 15 seconds to dispel any ice in the engine. This is required even in summer if the temperature is below 10C (EGNT :D ) and there is, say, rain.

Now, on odd days (like Friday 13th :D ) pilots SOMETIMES feel a LITTLE uneasy about runway length etc and MAY run up to around 70% before letting the brakes off. This obviously (as you said) gives you improved performance.

Surprisingly, for a flight to Iceland from EGNT, the runway MAY be a little limiting, due to either engine anti-ice requirements, low pressure, adverse winds or just a heavy aircraft. The crew MAY have felt easier by doing this run-up on that occasion.

ZTH - I guess no icing problem :D , but performance can be an issue expecially if you are going ZTH-NCL. The crew may, again, have felt easier with this.

Finally, it could have been some obscure technical procedure.

Many thanks for the reply.

Yes, it was coldish when we departed (5am!) from EGNT so that would explain it.

Cheers!

I recall once at LHR being advised of a 'warm up' period for the engines as it was the a/c first rotation of the day. For that, we actually parked at the CAT II hold point and engines ran at some power for over 30 seconds. Naturally, the a/c was shaking a bit! I suspect that there were other tech reasons for such a prolonged run.

Last Winter in Gothenburg, I was on a SAS MD83 and they did this on a very icy day. As they held against the brakes, the aircraft started to judder violently forward as, I assumed, the wheels started to skid on the ice.

However, my initial concern soon evaporated as I made my usual assumption that they knew what they were doing. I would have thought that any nervous passengers might have been worried though.

This might be a Islandsflug procedure on take-off, as I can recall the same happening at DUB last December on a 734.

BAe 146 :)

Alexandria to Heathrow is a good example, short runway, common to have adverse winds. Limited fuel uptake can mean diversions.

Paxboy, "warming up" a jet engine was something I always considered the preserve of AN 124's etc... ie not normal practice!

There was a time in the late 80's (88-89) when all BA 757's used to do an engine run at quite high power of about 45-60 secs at the hold prior to departure - something to do with a known problem on the then -535C engines which was put right by a mod. - still dont know full story on that one

Aircraft Brakes

Hopefully the day will come when most old pilots who were forced to use those terrible British designed air operated brakes will have left the system.

Most pilots today wouldn't dream of using the brakes of their cars the way they use aircraft brakes.

The pilot who runs up to take off power on the brakes and then lets them off in one hit is usually oblivious to the discomfort he imposes on everone else aboard except himself. With a modicum of skill he can flare the brakes off so that the pax don't have to do a quick retrieval of their heads and sundry loosley retained items..

The same pilot doesn't flare off the brakes just before a stop during taxying. Moans all round again. I wouldnt care to ride with him in his car either.

Come on pilots - I know most of you weren't taught to use brakes smoothly. The pedals aren't just ON/OFF toggles.

Good God, you mean we actually got the Slug away on time?:eek: Until recently, we didn't even have the crew at the aircraft until departure time.

I would have suggested it was simply the captain showing his frustration at yet another delay, and since no-one can see him shaking his fist from the threshold, he gives us a good blast with his noisy old engines instead.

Seriously though, he could quite easily be performance limited for a reduced power take off as the a/c is generally full (approx 170 pax or so with similar quantities of hold luggage) and with a fairly hefty fuel load (about 14t I think).

Mini wrote

As an air traffic controller I can assure you that we had (a year or two back)an instruction that Bmi a321's would require to hold before the first flight of the morning with power on to "bring the oils up to temperature"...so it seemed that they at least had it as normal practise. As for the Antonov...NOTHING they did was in the least normal ...a magnificent aircraft ..loved them!!

Come on Milt , don't spoil it for those of us who enjoy the "handbrake off" style departures. Not enough of them these days.

The AN124 - when I flew on it in the mid 90s the engines were spooled up to 80% and had to remain there for 4 minutes to heat soak the engines, before full power could be applied.

If this was not adhered to the result could have been fan blades on the taxi way. Might have been embarassing :D

It was interesting to gauge ATC reaction when the aircraft had to sit on the runway for this lenght of time

Not sure if the engines have been improved since then.

On the DC10 the cold weather procedure is to accelerate the engines to 57%N1 for 30 seconds every 60 minutes if excessve icing conditions exist and the rolling method of takeoff is the preferred. Because it may result in a slightly better takeoff performance

EW,

usually by the time the a/c has completed its taxi out the engines are ready to go. No expert though, this just based on observation.

Engineer,

Thanks for the explanation, have always wondered.

Magnificent piece of kit just the same, love the cranes.

It sounds similar to the noise abatement departure procedure used at John Wayne (SNA) LA California. Its a brilliant departure, engines spool up, brakes on...on...then release and off we go, it feels as if we are on the ground for a few seconds then sharp rotate, pushed in the seat, then level off, engines cut back...as we fly over the million dollar homes overlooking the pacific...

KP

With Avman on this one:

The sudden push back into beats any fairground ride. Nice reassuring feel that we are going to get past VR to V2 without any problems! :8 :rolleyes:

Three departues from Zakinthos, two in 737-400's one in a 757. Both times in the 734, the crew ran up to full (or high) power on the brakes and both times they made am announcement explaining that this was due to runway limiting factors. One guy actually went into quite a lot of detail about the combined shortish runway, high fuel load and high temperature which I found interesting as a kid longing to learn to fly. Not sure how this went down with the more nervous pax. who no doubt had visions of us just mking it off the ground before the beach at the end of the runway. No such problems with the 757 though.

As posted by Engineer

The AN124 - when I flew on it in the mid 90s the engines were spooled up to 80% and had to remain there for 4 minutes to heat soak the engines, before full power could be applied.

Yep we still do it that way!!! although the TBO has been extended now:ok:

VEEPS :D

Long time ago, watched one at SNN preparing to go west a long way, did exactly as above, then was cleared for take off, with a request, "call passing through 1500 Ft".

Off it lumbered, eventually, in a large cloud of spray from a very wet runway, and fairly quickly vanished into the murk. Well, I listened to the decreasing engine noise, then after a while thought, "oops, he's forgotten the 1500 Ft call". Wrong.

After close on 7 MINUTES, he called passing 1500 Ft. I don't know what weight he had there, but it had to be real Heavy!!!:O

(edited to correct typo's)