De-rated departures, a risk to safety

[missy]

I ask, Are de-rated departures a risk to safety?

Your thoughts...

[mono]

No.

Why should they be?

The throttles can always be firewalled if need be, and the derate calculations take into account conditions and available runway.

[West Coast]

Missy
There are a number of considerations given prior to using flex power. Wake turbulance from preceeding aircraft(not used if prior ac is a heavy or 757) weather, runway conditions and length, terrain and obstacles, special departure proceedures, aircraft status, such as an anti skid channel is deferred, certain flap settings peclude its use, tailwind componants. There are a few more but I don't have my SOP in front of me.
That said, I estimate around 3/4 of the time we use flex. As mentioned by Mike, they are good for the engines. I have never actually seen it, but hear often of a study in the US I believe that has shown there to never have been an engine failure during a flex departure.

[missy]

I might be missing something here but wouldn't a derated departure use more runway than a "normal" departure, thereby increasing runway occupancy times?

[cphflyer]

Yeah sure a derated Thrust T/O will use a tiniewinie bit of extra tarmac...... not much though versus a full power on the brakes which on powerful underslung engined a/c may in fact start to pick up bits of threshhold!

Speaking ISA conditions B757 Wt of 90 t will still climb out on a derated Thrust @ about 3000fpm!

Full thrust will only coz a few busy moments. With over pitch (company limit) of 20 degrees to keep our V2+20 which keeps our neighbours happy and keeps our (company) climbout noise abatement procedure. Then u got an early Altitude Capture which unless uve selected Climb Thrust will see u accelerating thru 350 kts very quickly as u retract the flaps, checkin with Atc and I could go on and on and on.

I do derated thrust T/O everywhere unless Safety dictates it or Mel item or If windshear/Cbs close by / observed or reported.

I like to keep life simple! Never had this problem on TurboProps!

Hope that helps.

[A/P Disc]

Mono,

you can't always firewall the engines
during a flex/derated T/O.

If you have a Vmcg limited T/O and
you lose an engine you cannot
firewall the remaining engine.You will
depart the runway pretty quickly then.
The performance calculations do not
cater for this situation.See Boeing training
manual 757/767 p2.16.

Rgds

[Scott Voigt]

Well there are derated and then there are really derated after departure. Take a look at what they do at KSNA for a departure for noise abatement. That I would call close to unsafe due to the slowness of the aircraft and the configuration that you have to fly in. If you lose one on departure, it is going to be a LOT of fun in the cockpit...

regards

Scott

[West Coast]

Scott
Not sure what your getting at, any engine failure off any runway at any weight will ensure a bust cockpit. Reduced numbers still allow compliance with all far25 requirements, plus additional thrust is but a push away. That said, I am no fan of the departure out of SNA. If I don't my brother who lives near back bay Newport will be sure to call in a noise complaint if the monitors don't get to me first

[squeaker]

On the 757 we hardly ever do full power takeoffs, usually only when the engineers want one. More often than not we can use max reduction. As Mike J said, I think it would only enhance safety as the figures are based on the reduced thrust and there is more available if you need it, plus less wear & tear on the engine. On another note, with a full power takeoff, when you reduce to climb thrust, in the cabin it sounds like the engines have stopped- poor punters generally scared fartless!

[Fox3snapshot]

Does the derated departure only focus on the actual take off....my understanding is that it is right up through to the TOPC(index/cruise climb?????).

If this is the case then I certainly have something to comment on from an ATC and safety point of view (the Airbus 340 will be my first slamdunk if this is the case !!). If not, then I will keep my gobby gob shut.

Fox3snappy

[Scott Voigt]

WEst Coast;

I've been looking at some data that and NASA reports that have shown that to fly the departure correctly, you have to make some huge safety trade offs for the departure. I just don't like to be going that slow in the event that you lose one. You have very little time to recover.

regards

Scott

[max AB]

Flex/Assumed temp T/O actually have increased margins as the stop distance is calculated on the TAS (assume nil wind) at the higher temp not the actual temp. So e.g at ISA if V1 was 140IAS then the stop calculation is based on 140TAS, if you assume a temp of 60C then TAS used will be higher around 155 (guessing here). V2 margin is increased also as it doesn't take as much energy to accelerate as is assumed at the higher temp. So Missy not withstanding the limitations mentioned by others as to when you can use a reduced thrust T/O, they do not have a reduced safety margin, yes a bit more runway used. Fox3 some jets can reduce their climb thrust as well for the same engine longevity reasons as Take Off. I would say most companies that do this would allow it below certain weights only, so you are not likely to see any huge variety in climb rates as a result. No more a variety than a heavy 340 vs a light one.

[Fox3snapshot]

Thanks AB, unfortunately the older mark Airbus aircraft (excluding 310's which climb like rockets) are absolute dogs for climb.....which in our business works against them as you can't afford to have them climbing through all your traffic and airways when its really busy.

So utimately if they can't meet the requirements (often the case) they don't get the level....not sure Mr and Mrs Engineer think of this when designing the ultra efficient engines/airframes!! In reality the quicker you can get there the better in the busy sectors.

[West Coast]

Scott
Don't think in terms of time when thinking about an engine failure in a FAR 25 aircraft. Think of altitude. I am guaranteed certain performance if I follow the profile, no matter where it fails. If by the time a FAR25 aircraft pulls back, it has cleaned up in large part to probably its smallest flap setting( somewhere around 6-12 degrees) or zero flaps.
A 757 lost one out of there just a few years ago, rained the golf course with parts, other than that no problem.
I don't like the departure, but it has nothing to do with reduced thrust departures.