Tee Emm
20th May 2009, 11:24
Discussion came up in the simulator on B737 unusual attitude recovery technique. Specifically where the FCTM under Non-Normal Operations page 8.32 "Flight Path Control", states: "...this may require use of unusual techniques such as the application of full aileron or rudder...the objective is to take whatever action is necessary to control the aircraft and maintain a safe flight path..."
Elsewhere, at page 7.25 and 7.26 (FCTM) the discussion talks about high bank angles.
One extract says: .."If full roll control application is not satifactory, it may be even necessary to apply some rudder in the direction of the desired roll.....only a small amount of rudder is needed....too much rudder applied too quickly or held too long may result in loss of lateral control". A charming thought, I'm sure.
Let us assume for the purpose of this discussion that due to mis-handling, the 737 enters a spin. Presumably the pilot would take standard spin recovery action. Those readers who have not spun ab initio training aircraft, need to read up on spinning as it is not the intention to teach such things here.
Included among other coordinated recovery actions, is putting in full opposite rudder to the direction of the spin. However, if full rudder is not available due to the Rudder Pressure Reducer operation then this gets awkward and things could rapidly get out of hand, if they haven't already!
You need all available rudder to counteract the yaw in the spin. How to get it? The RPR causes the hydraulic pressure to the rudder to be reduced when the aircraft climbs above 1000 ft. It reduces rudder authority by about one third. But you need the full rudder pressure back in order to get more rudder deflection to aid spin recovery.
According to the FCOM, hydraulic pressure returns to normal when the aircraft descends through 700 ft agl (bit late to recover from ensuing dive at that point). The hydraulic pressure to the rudder also returns to normal if "B" hydraulic system depressurises - or whenever the N1 difference between the left and right engines exceeds 45% N1. The problem with the latter is that with one engine at closed throttle idle of 32 percent N1 - (or greater N1 at high altitude), you need at least 77 percent N1 on the other engine in order to achieve the required 45 percent N1 difference
.. Or maybe you could quickly close down one engine causing its N1 to rapidly wind down and now the 45 percent difference between the two engines will mean less thrust can be used on the live engine. If you don't opt for that choice, then depending on the direction of spin, that means you could have quite high thrust on one engine - which in turn could either aid or hinder spin recovery. That is because standard spin recovery normally involves closing both thrust levers.
So it becomes a bit of a problem. That leaves only the Hydraulic B System pumps off, to knock out the RPR and allow more rudder deflection, doesn't it? Or does it? Remember, the availibility of that extra third of rudder deflection could make all the difference to the outcome.
Any thoughts on the above? :ok:
Elsewhere, at page 7.25 and 7.26 (FCTM) the discussion talks about high bank angles.
One extract says: .."If full roll control application is not satifactory, it may be even necessary to apply some rudder in the direction of the desired roll.....only a small amount of rudder is needed....too much rudder applied too quickly or held too long may result in loss of lateral control". A charming thought, I'm sure.
Let us assume for the purpose of this discussion that due to mis-handling, the 737 enters a spin. Presumably the pilot would take standard spin recovery action. Those readers who have not spun ab initio training aircraft, need to read up on spinning as it is not the intention to teach such things here.
Included among other coordinated recovery actions, is putting in full opposite rudder to the direction of the spin. However, if full rudder is not available due to the Rudder Pressure Reducer operation then this gets awkward and things could rapidly get out of hand, if they haven't already!
You need all available rudder to counteract the yaw in the spin. How to get it? The RPR causes the hydraulic pressure to the rudder to be reduced when the aircraft climbs above 1000 ft. It reduces rudder authority by about one third. But you need the full rudder pressure back in order to get more rudder deflection to aid spin recovery.
According to the FCOM, hydraulic pressure returns to normal when the aircraft descends through 700 ft agl (bit late to recover from ensuing dive at that point). The hydraulic pressure to the rudder also returns to normal if "B" hydraulic system depressurises - or whenever the N1 difference between the left and right engines exceeds 45% N1. The problem with the latter is that with one engine at closed throttle idle of 32 percent N1 - (or greater N1 at high altitude), you need at least 77 percent N1 on the other engine in order to achieve the required 45 percent N1 difference
.. Or maybe you could quickly close down one engine causing its N1 to rapidly wind down and now the 45 percent difference between the two engines will mean less thrust can be used on the live engine. If you don't opt for that choice, then depending on the direction of spin, that means you could have quite high thrust on one engine - which in turn could either aid or hinder spin recovery. That is because standard spin recovery normally involves closing both thrust levers.
So it becomes a bit of a problem. That leaves only the Hydraulic B System pumps off, to knock out the RPR and allow more rudder deflection, doesn't it? Or does it? Remember, the availibility of that extra third of rudder deflection could make all the difference to the outcome.
Any thoughts on the above? :ok: