Originally Posted by
interpreter
Why at 600 feet was there a need for additional thrust? If the aircraft was at that stage being flown manually (I believe it is normal to disconnect the autopilot at approximately 1000 feet) had the sink rate become excessive and a need for more thrust? ............
It is common practice at busy, large airports to maintain a high-ish approach speed on final approach, typically 160 to 170kt - until 4 nm from touchdown. The gear would normally be up and the flaps at one of the early to intermediate settings (sorry, I donīt know what settings the 777 would use but on the VC10 I flew in the RAF it would have been the first stage, called "take-off" by Vickers).
At 4nm, the gear would be lowered and the flaps extended to reduce to "normal" approach speeds (again, Iīm not familiar with the 777 but the VC10 would have been about 120-130kt).
There are a number of reasons for the high speed approach including: all aeroplanes flying similar speeds for easier ATC spacing and low drag configuration allowing lower power settings, lower fuel usage and less noise.
The downside is that the aeroplane is not placed into the landing configuration until late on the approach and as the drag increases (gear/flap extension) thrust has to be increased to compensate. Normally, everything should be settled by 500' above aerodrome level (aal) - unless, of course, the engines fail to spool up when requested - then it becomes "interesting"! If not stabilised by 500' aal, then the normal procedure would be to execute a go-around.
Hope that helps.
EDIT: Because my post seems to have upset M.Mouse so badly, may I reiterate that I am simply quoting an example of how an aeroplane with which I am familiar would fly "160kt to 4nm". Barring differences in terminology between manufacturers and differences in speed between types, the principle hold good.
I was trying to explain how an aeroplane could end up in a position whereby a power increase was needed late on in the approach and believe that the information posted above is relevant for explaining a PRINCIPLE. What I am NOT doing is passing comment upon this incident.
In addition, M.Mouse, whilst I donīt pretend to be familiar with the 777 I am reasonably familiar with BA shorthaul operations having spent 6 years teaching the self same BA SOPs to BA shorthaul cadet pilots.
Whilst the 777 may be different, last time I looked in BA FCOs, the SOP requires that if the approach is not stable by 800' aal then "consideration" should be given to the option of exectuting a go-around and Missed Approach Procedure and that if the aeroplane is not stable by 500' aal then the crew "must" go-around. Therefore, the required power increase may quite legitimately be made very late on in the approach - and whilst 600' is a bit on the late side, it's still (just) IAW SOP.
I'm quite happy to be corrected if wrong.