ImbracableCrunk

I had a sim session a few days ago and we were working on the inflight restart and came across this:

I can understand why oil pressure would be low, but not why oil quantity would be zero. Any ideas?

aerobat77

never flown the 737 but when i remember right from my bae146 time the amount of oil in the pump sumps is a function of rotor speed . the quantity is metered in the sumps not the oil tank and when the engine is standing still the sumps are nearly emtpy and the oil is in the tank.

but not 100% sure here.

STBYRUD

Hmm... the CFM56 reads oil quantity when the engine is shut off since it is measured in the tank, in fact that is the only time the indication is reliable (from between five to thirty minutes after shutdown if Memory serves me right). Anyway, it is also very temperature dependant - maybe the cold soak inflight with the engine off can lead to such a low indication? Just guessing here, sorry :/

grounded27

2nd hand info B742. Noticed signifant loss of oil quantity, shut down said engine, on approach restart said engine hoping there would be enough oil remaining to land, if not, crew was prepared for failure. They saved an ace in the hole. Suppose much different with a 2 man cockpit to manage and yaw MGT on a two hole aircraft.

aeromech3

On most Turbo Jet engines for an accurate reading the oil quantities level should be checked soon after engine shut down (notable JT8D's and RB211 types). Reason: the oil can migrate out of the 'tank' into the gearbox, similarly, in a windmilling engine at low N2 the oil pump scavenge is inefficient and the quantity indication from the tank will decrease despite there being adequate oil in the engine.

Mr Levitator

For 73 3-5 series, the oil qty will vary depending on temp, coldsoak and time since shut down. In my experience tho variance will be 3-4 ltrs maxim. There should always be a significant qty showing and at least the min recommended for eng start (a lot less than the scope of normal operating qty's including variances). I believe that the eng 1&2 oil qty are both supplied by the same power supply, there fore, if one eng is registering a +ve qty, the other is powered (but not necessarily receiving valid data). You will then have to decide is you have a case of invalid/nonexistent data to gauge (some have a light blue off scale fail needle index) or a correctly indicated low qty.

Restarting a oil deprived CFM56 will quickly (5-10 mins) lead to the most expensive auto shutdown you will ever see on a 73. Having said that, as a last resort thats 10 mins of thrust which you might not otherwise have had!

Hope that helps? Typed after a busy day.......

Mr L

M.82

My friend,

I found this at FCOM VOL2, page 7.20.10.

¨Inflight Starting

Note: At low N2 values (¨RPM below 8%¨), the oil scavenge pump may not provide enough pressure to return oil to the tank, causing a low oil quantity indication. Normal Oil quantity should be indicated after start¨

Page 7.11.17

¨ Note:Indicated oil quantity may decrease significantly during engine start, takeoff and climb out. If this occurs, ENGINE OPERATION IS NOT IMPACTED and the correct oil quantity should be indicated during level flight¨

Check quantity before start, check pressure after start and
ENJOY NG!


I hope it helps

ImbracableCrunk

Thanks, guys. These are the answers I was looking for.