787 take-off performance
 

I live a few miles north of Gatwick so I see aircraft after they have taken off and turned 180* to the north.

I've long thought that 787s appear to be very low. I've recently taken up cycling and passing the end of the runway, it looks as if 787s clear the trees outside the airport's fence only by a wingspan. I've observed two (TUI and DY) whose main wheels left the runway 7 & 9 seconds before flying over the end of it; and on FR24 I've noted a 787 at 1000' where the preceding Airbuses were at 2000'.

Surely they can be more sprightly than this - what advantage is there in trimming performance so much more than other aircraft do?

I'm sure I'm entirely wrong, but it seems to me that an engine failure on such a slow take-off must be more hazardous than when both engines are already on full power, particularly when there are trees at the end of the runway.

I'd suggest that what you are seeing is aircraft using a de-rated (i.e. not full power) take-off.

Gatwick (like Heathrow) operates a "1,000 feet rule", meaning that aircraft must be at that height (or higher) by the time they are 6.5 km along track, measured from the start of their take-off roll.

In addition, the EGKK SIDs specify a minimum initial climb gradient of 5.5%/5.2% to 200'/600' QFE for 08 and 26 takeoffs, respectively.

Provided a departure meets those requirements (which are closely monitored) then there is no cause for alarm.

Have a read of this: Gatwick Airport flight performance team report 2016

It must be de-rated, given what we see at Farnborough.

But why choose to climb so slowly? I thought the point was to get as high as possible so as to reduce fuel burn.

Like many things in aviation, it's a trade-off.

De-rated takeoffs = reduced engine maintenance costs.

Fair enough. You must be right; it still seems an oddity.

I was going to ask almost the same question. I've noticed the Dreamliners (usually at LHR) seem to climb at a lower pitch than other aircraft. I assumed it was a passenger comfort thing.

What you see at Farnborough is also missing about 80 tonnes of fuel, 250 passengers and 20 tonnes of LD3s in the hold.

The 787 has a very leisurely climb out, it's always later and lower than the 777 on an equivalent routing, it's rather reminiscent of the original A340s.

All good points about engine derating, but they do this for other aircraft as well which doesn't explain the relative lethargy on the climb rate surely?

On previous types (737, 747, A320) we used full thrust for take-off, derated (or 'flexed' in the case of the A320) by using the Assumed Temperature Method (ATM).

This results in a take-off thrust known as 'D-TO' with an associated assumed or 'flex' temperature. In broad terms, the longer the runway, the higher the temperature and the lower the thrust. Regulations limit the thrust reduction to a maximum of 25%.

The Boeings also had the ability to use a fixed de-rate of 10% or 20% which was useful on short contaminated runways where Vmcg might be limiting. These settings are known as TO1 and TO2.

The 787 is the first jet I have flown which routinely combines both techniques. We can take off with TO, D-TO, TO1, D-TO1, TO2 and D-TO2.

The combinations of ATM and fixed derates (D-TO1 and D-TO2) give a very low thrust setting for take-off which results in much cooler EGT and thus extends engine life as well as improving reliability and reducing the overall chance of an engine failure (fleet-wise).

As far as I know, the 787 is the only big jet which uses this technique which is why it appears to climb at a shallower angle than other jetliners.

As an interesting comparison, using reduced thrust, the target all-engines pitch attitude on a 737 or A320 on initial climb is about 16-18*. For a 747 it is about 15*. For a 787 it is about 10*.

And is there really no increased risk in aiming only narrowly to clear the trees at the end of the runway?

I live close to Heathrow and the 787 and the A380 fly low and slow and quiet, both are magnificent and a real improvement for local residents

The sooner that noisy 747 monstrosity is out of service the better

Burn him, he's a witch��

EGLD

Why do you live close to Heathrow and moan about the noise. There have been noisy jets there since the early 1950s.

p.s. If you have lived there since the 1940s then maybe you have a point and I apologise!

The OP simply pointed out, quite correctly, that the 747 is considerably noisier than the A380 or 787. Do you dispute that ?

Not disputing the noise difference, but he did call the 747 a "monstrosity".

I think it has been "Queen of the long haul skies" for more than 45 years!

Where I live we have a 747-8 VIP machine that is no noisier than the 737-800.

That's to be expected - an aircraft in VIP configuration will typically be a lot lighter than the same aircraft full of pax or cargo, and consequently a fair bit quieter.

The ICAO certificated flyover noise level for a B748 at max weight is about 6 EPNdB higher than the B738, so roughly 4 times as noisy.

Good point Dave. I think it positions empty to pick up the VIPs, so probably max flex even off 7000 ft runway.