quiones,
My first choice , if between MED and MAX brake is required would be to look for another airport to land at. But each crew has their own opinion about that sort of thing.
Dragon 1
Sorry you felt I was "'giving you a flying lesson". That was never the intent. And, as you have reminded us the topic is hot brakes vs max reverse and the effects thereof.
The numbers you have put out do not reflect the reality of line operations. They are determined with the following conditions;
1. Speed at the threshold is VLS
2. Altitude at the threshold is 50 feet agl
3. Thrust levers to idle at 50 feet agl
4. Very little flare
5. Auto Spoiler deployment
6. Max brake applied and held until a complete stop
The time available for reverse to work in this situation is minimal and therefore the the one percent reduction in actual stoppping distance.
But in line operations we do not apply and hold max brake for landing. The reason of course is that the fuse plugs would melt, the brakes would probably seize and the chance of a brake fire is greatly increased.
Therefore the distance saved by using max reverse in line operations is much higher than the distance saved in the certification tests.
There is no doubt that Flap 3 approaches and landings save fuel. Idle reverse saves fuel and noise. But brake temperatures will rise to above 300 very quickly since they are providing the bulk of the deceleration. Does this impact the life of the brake ... of course it does, but the mob that I worked had leased brakes so did not care about shortening their useful life. The cost of fuel and engine maintenance was less than the cost of changing out the brakes.
regards,
Bruce Waddington
edited for grammar, not content
Last edited by Bruce Waddington; 28th Apr 2009 at 04:29.