747-400 Wet stopping distance
Thread Starter
747-400 Wet stopping distance
Would some kind soul with access to a 747-400 perf manual let me know the Accelerate-stop distance differences for a given set of conditions between wet and dry? Is there something odd about the procedure that makes the wet distance more than 20% greater? Does wet not use reversers? The distances in the Sim seemed wrong and wasn't sure if there was something unusual in the Regs that don't apply to the 2-engined jets I usually operate.
Many thanks
Many thanks
blue up,
Considering industry wide observations and discussions on the generic subject, you might better conclude that the simulator model is incorrect
What is the perf basis of your operational data; manufacturers actual ‘actual’, or more recent FOLD. Third party data - similar questions, what do they use, or assume.
What data is the simulator based on; compare assumptions, braking action vs water depth, runway surface, … ,
Considering industry wide observations and discussions on the generic subject, you might better conclude that the simulator model is incorrect
What is the perf basis of your operational data; manufacturers actual ‘actual’, or more recent FOLD. Third party data - similar questions, what do they use, or assume.
What data is the simulator based on; compare assumptions, braking action vs water depth, runway surface, … ,
Thread Starter
ISA conditions for any given weight would be OK. I'm after finding out what the percentage difference is between wet and dry and then what reverser usage is assumed to make that calculation. 3 reversers, 2(symetrical) or none for the wet case.
For planning purposes the charts show a 300 tonne airplane requiring about 8000 feet for dispatch to a sea level airport with no wind and normal brakes on a dry runway and about 9200 feet on a wet runway. So the plane should be able to come to a stop in about 4800 on a dry runway (60% of 8000). The extra 1200 is the additional 15% to release the aircraft to a wet runway.
The unfactored advisory landing distances get interesting. There are tables for a dry runway, good braking action, medium braking action and poor braking action. For a 250 tonne aircraft both the dry chart and the good braking action chart show the aircraft stopping in 6420 feet with auto brakes 3 and flaps 25. In both cases you must add 80 feet if only two reversers are working and 110 feet with no reverse. It would take 6770 to stop on a medium braking action runway and you must add 460 feet for two reversers and 1810 for no reverse. And on a runway with poor braking action it looks like you'll need 7860 to stop and you must add 1550 for two reversers and 5040 for no reverse.
Working the advisory distances at 300 tonnes it looks like with max autobrakes the aircraft should stop in 4600 feet on a dry runway which validates the dispatch numbers. On a wet runway with good braking action it should take 4950 to come to a stop. But on a runway with poor braking action a 300 tonne aircraft will need at least 8000 feet to come to a stop.
Hope that helps.
The unfactored advisory landing distances get interesting. There are tables for a dry runway, good braking action, medium braking action and poor braking action. For a 250 tonne aircraft both the dry chart and the good braking action chart show the aircraft stopping in 6420 feet with auto brakes 3 and flaps 25. In both cases you must add 80 feet if only two reversers are working and 110 feet with no reverse. It would take 6770 to stop on a medium braking action runway and you must add 460 feet for two reversers and 1810 for no reverse. And on a runway with poor braking action it looks like you'll need 7860 to stop and you must add 1550 for two reversers and 5040 for no reverse.
Working the advisory distances at 300 tonnes it looks like with max autobrakes the aircraft should stop in 4600 feet on a dry runway which validates the dispatch numbers. On a wet runway with good braking action it should take 4950 to come to a stop. But on a runway with poor braking action a 300 tonne aircraft will need at least 8000 feet to come to a stop.
Hope that helps.
