Originally Posted by
CaptainSandL
The flap load relief function is controlled by the FSEU. This receives airspeed information from the left ADIRU. This gets static & pitot pressure inputs from the left air data modules (ADM).
So, if the Capts pitot probe and/or static port are u/s, the flap load relief function will not be available. This does not prevent you from using flaps but you will have to monitor airspeed from the F/O’s instruments.
Well, consider an erroneous overspeed indication on the Captain's side, due to incorrect inputs to the left ADIRU. If the FSEU uses this incorrect airspeed, then I would imagine that the flap load relief system will prevent the flaps from moving beyond Flaps 25, even if in reality the flap placard speed is not exceeded. Unless the FSEU disables the flap load relief function in case of an IAS disagree. Does it?
Your scenario of extending the flaps “far into the red” is, I would hope, unlikely as you will have noticed the high speed from other clues - F/O’s insts, airflow noise, control feel etc. If you were to extend flap at high speed you would run the risk of damage or detachment which, if asymmetric, would cause large amounts of roll.
I see I wasn't very clear in my first post. The scenario I intended to describe does not involve an
actual overspeed situation, just an erroneous overspeed indication on either the Captain's or the F/O's side. This could happen if a static line gets blocked during descent (sensed static pressure too low -> computed dynamic pressure too high -> computed IAS for the affected side too high, rising "far into the red" if you descent far enough). Of course, this would also cause an altitude disagree, with the indicated altitude on the affected side being 'trapped' as well.
I have not got the link to hand as I post this, but search the internet for “N520UP AAIU Report No: 2004-004” which describes a 747 with static port problems on a post maint airtest.
Thanks, this could be helpful!
Originally Posted by BOAC
The simple answer is Flap15
Absolutely, but it is always nice to be prepared.
If the flap load relief system is inoperative in case of an IAS disagree, then there is no problem. But if it isn't, I'd rather know in advance if flaps 30 or 40 will not be available than to find out during final approach. After all, some runways are better suited than others when it comes to flap 15 landings.