Boeing 747-400 Flap Load Relief
 

Good evening colleagues,

I just encountered a problem I couldn´t solve for the moment.

The 744 has a flap load relief function, so if you are in configuration 30 they retract to 25 if you pass the red band by more than 5 kts.

But in case of an unreliable airspeed you cannot thrust these red bands, so what will happen with that flap load relief when all the three airspeed indicators are lost?
Will it work, and based on which speed? It can´t be the groundspeed because the aircraft cannot correct it with the present wind!


P737!

Clearly got an issue with Mircrsoft Flight Simulator???:ok:

aa) The 'Airspeed Indicators' have no influence on this, the only display is a computed airspeed tape on the Primary Flight Display. The display does not influence the flaps.
bb) The aircraft has 3 ADIRUs to compute the Airspeed to display (except the Stand by Indicator which has a direct Pitot and Static line (not on all B744))..and 3 Flap Control Units to sort the flap position. Airspeed data is fed to the Flap control units and many other systems by ARINC 429 data bus from the ADIRUs.
cc) Where would Ground Speed come in to this? The issue is Dynamic pressure on the Flaps for structural concerns so only the 'Indicated' IAS or more likely CAS would influence this.
dd) If all 3 are lost then fly very carefully, and there would be no overspeed protection....probably the least of your worries at that time!

Hey spannersatKL, you funny guy.

Maybe my question was misleading.

The flaps´ only reference concerning flap load relief function are that red bands? This is not really mentioned in the Volume 2, where flap load relief is just a very small subsection.
In this case you could with unreliable airspeed never extend your flaps to 30, because you are (with 3 false indications on all the three speed indicators) always within this red band.
And the aircraft did not know you are within an unreliable airspeed.

So whats the reference for the flap load relief function?


P737

Long time since I worked on the 744 but I believe that if the FCU's have invalid speed data, an EICAS status message is displayed and flap load relief is inhibited.

According to my engineering training notes, a Status Message "FLAP LOAD RELIEF" appears if Air Data is lost (I assume this signifies that the function is lost).

My notes only mention specific airspeeds. They may or may not correlate to PFD red bands. There is hysteresis in the logic. The flaps do not return to their original positions at the same speed as they started to retract.

Rgds
NSEU

ADIRUs on 744s, Spanners??? :}

Apologies NSEU! IRS... You are right. My bus training getting in the way! Havn't touched a 744 for a year or 5.....

Sorry to hear that, Spanners :) I dread the day I'll have to move on to Airbuses and the like. :}

A bit of sentiment here, cut my teeth on the 742 as a young line/avionic tech. Would seem logical that NCD would negate protection in modern aircraft. Makes me think of the 727 and DC-9 that had seperate pitot probes for elevator load feel (different issue).