View Full Version : pushback engine starts

3rd Jul 2001, 01:44
While watching the jets being pushed back, I noticed that's when the engines are started.

The ground crew are usually walking right by the nose of the aircraft.

Just how close to those engines is safe for someone to be when the engines are started / running ?


3rd Jul 2001, 02:22
The maintenance manuals for the B757 and B767 shows a hazardous area infront of the engine of approx 9feet in radius at idle power, extending to 16ft at breakaway. The more dangerous end in my opinion is the hot end,the exhaust, with very fast hot air, creating a hazardous area over 400ft behind the aircarft.
There is a safe entry corridor to get access to the engine when running, usually reached down the centreline of the belly of the aircraft, then walking at 90 degerees to the engine, staying away from the intake, this allows maintenance staff to carry out tasks such as manual starts and leak checks on the core of the engine, at idle power only.

Yeap, yor right Captain, it is broken..I'll get you an engineer

3rd Jul 2001, 10:17

So how close to the front of the engine can you get ? ... 9ft at IDLE, ... 16 at 'breakaway' .. what is breakaway ?
(minimum thrust to start moving/taxiing ?)


3rd Jul 2001, 11:52
If you run the engines at idle power, what percentage of max power is set? 10-15%???
If say for instance on the B777 etc (big twins) with the Trent 800 engines, rated at 90 000 lbs of thrust each = total 180 000 lbs, you run at 10% idle power, you still putting out 18 000 lbs of thrust???
That is more than old Bac1-11's at full cruise power. Is my assumptions correct?
What is the situation on your fleet and is there a max setting for idle runs?


3rd Jul 2001, 18:37
RR Trent 800 idles at around 19-20% N1.
But this does not mean that the engine is producing a fifth of its rated thrust at idle.
% for N1,2,3 is only an indication of blade speed. I remember reading somewhere in the AFM that N1 can achieve about 2-3,000 rev per minute. So a reading of 20% N1 means that the blades are doing 400-600 rev per minutes.

3rd Jul 2001, 19:13
Given that lift from an aerofoil is proportional to the square of speed, I guess the thrust provided at idle would be a much lower level than you suggest. Of course the number of aerofoils in an aero engine makes things even more complicated (rotors and stators) so I dunno, but thats my guess.