A320 CFM56 Fuel flow during des. q.

[tom775257]

Hi,

A question about something that happened last night on an A320. We were descending at 300kts at idle, and I happened to notice the fuel flow on engine 2 was zero. There was no warning, I guess I just glanced at the EWD and noticed. Anyway perhaps 5 seconds later the fuel flow increased again and continued as normal for the remainder of the flight. A quick glance at the EGT and it looked fairly normal.

The CFDS had no warnings for the leg, no messages were produced by the ECAM/FWC. Basically any ideas what happened? I guess there were two options. i) Fuel flow reading was incorrect (unlikely without a warning I suspect). ii) Guess work on my part but from what limited knowledge I have of the FADEC/systems on the CFM565b4 (only a pilot) - the ECU detected a pressure/temp situation it didn't like and decided to remove fuel (perhaps detected flameout?) and re-introduce to let things stabilise all without deciding it necessary to inform perhaps the aircraft or perhaps the aircraft decided not necessary to inform the pilot. (Remembering the auto-relight function)

Cheers, Tom.

[Gary Lager]

Have sen this a few times, the first worried me, subsequent times I resorted to stage 3 of airbus flying "it does that sometimes".

I understand that the FF indications don't show values below 150kg/h, if the measuremnent drops below this value then it displays zero, then picks back up after a few sec.

Watch it on engine start, it does the same thing - the first indication you get is about 180kg/h.

There's surely someone else out there with more technical info on this, though...over to them!!

[Right Way Up]

Possibly covered by TR 2-1 (Oct 2005). "Fuel flow indicating zero at TOD"
Can last for some minutes!

[Down Three Greens]

The Fuel Control Unit will force the fuel flow indication to zero when it detects the main fuel valve is closed. As the FCU gets older with wear and tear, the valve will think it's totally closed when it is at very low flow rate, hence you will see a zero fuel flow indication in the descent. A new FCU part is available but the unit is still technically servicable.

There is an Airbus Telex covering the issue.

DTG

[tom775257]

OK thanks guys