Main Checklist - Engine Shutdown
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It was mentioned recently in a thread on Falcon Online that the BMS checklist has as an item on the engine shutdown checklist, ENG FEED Switch - Set OFF. This was discussed, as it seems to be BMS specific, and is omitted in other dash ones and dash one checklists. Some dashes even describe the switch in question as being safety wired shut, so that it is only toggled in an emergency. What is the purpose of it being included in the BMS procedures? Is this due to a modelling limitation?
Cheers!
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There should be no reason to turn the ENG FEED knob to off before shutting down. At least in PW 220 engine, imagine a GE shouldn’t be different.
At the same time there should also not be any wiring on that knob as you’ll need to move it if you are fixing a fuel imbalance.
A knob that does often have wiring is the Fuel Master Switch, even though it also has a guard. You really want to make sure you actually intend to move that one to its off/closed position.
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Consistency reason
Since the cockpit checks and the verify checks have it set to NORM before starting. (And since default ramp start have it OFF and ramp start requires to be moved it to NORM) The shutdown has it to OFF as well - that way the pit is found always in the same state from shutdown to prestart
regardless of doing it or not has no impact in BMS at shutdown obvioulsy - unless you use a physical pit where finding the pit in the same state from shutdown to prestart is desirable. -
There should be no reason to turn the ENG FEED knob to off before shutting down. At least in PW 220 engine, imagine a GE shouldn’t be different.
At the same time there should also not be any wiring on that knob as you’ll need to move it if you are fixing a fuel imbalance.
A knob that does often have wiring is the Fuel Master Switch, even though it also has a guard. You really want to make sure you actually intend to move that one to its off/closed position.
In fact, the Fuel Master Switch is the one often described as having safety wire. I made a mistake there.
Although, the wire should not prevent you from rapidly moving it as required.
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…in the RW - and based what I know about the F110 - one shouldn’t cut fuel feed to the engine until it has stopped rotating. But it is acceptable (and probably wise) to stopcock the fuel flow at shutdown…I know a couple platforms that have such knobs/levers and some that have shutoff valves implemented automatically, as system pressure decays.
Stevie
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I’m not convinced that “for consistency” (returning to the initial state) is a good argument to do a certain action on a checklist. It’s even possible that receiving the jet with the feed knob off might be atypical R/W.
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…I doubt that.
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In the real world it’s about 50/50 if the knob is in norm or off. Depends on what checks/work maintainers have done in between flights (for some stuff they turn everything off and some stuff they don’t).
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This, I will believe…
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…in the RW - and based what I know about the F110 - one shouldn’t cut fuel feed to the engine until it has stopped rotating. But it is acceptable (and probably wise) to stopcock the fuel flow at shutdown…I know a couple platforms that have such knobs/levers and some that have shutoff valves implemented automatically, as system pressure decays.
Eng feed to off does not stopcock fuel flow anyway. It controls power to the fuel flow boost pumps, but the siphoning system is always active regardless of eng feed knob position.
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Eng feed to off does not stopcock fuel flow anyway. It controls power to the fuel flow boost pumps, but the siphoning system is always active regardless of eng feed knob position.
Which in the case of the F110 could do some damage…if the fuel flow is restricted in any way. Fuel is used to cool some on-engine systems - including electrical ones. Depending on just what gets restricted when you can risk possible overtemp of some of those systems. You never want to let the the engine run dry…which I’ve always wondered - what is the usual min on-deck fuel state for a Viper?
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The siphoning system is always active regardless of the eng feed knob position - so long as at least one reservoir tank has no air in it, the FFP will still be getting fuel flow, even with the eng feed knob in off, and the DEC will still be getting fuel for cooling.
The fuel system displays usable fuel, so a totalizer reading of 0 lbs is the minimum operating fuel level.
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…first thing I ever learned in flight training was that all fuel indication systems lie.
It’s flow that’s important in this case, not quantity.
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Well its not going to indicate perfectly like it does in BMS, not during maneuvering flight…
USAF regs have minimum fuel level permissible for landing as being 1000 lbs - I vaguely recall reading somewhere that the 8 FW regulated bingo was 2400 lbs? IIRC that was so you could make it to Osan in case there was an emergency and the ALS could not be set up in time, and still have more than emergency fuel over Osan.
Back on the topic of the DEC getting adequate cooling, it still gets fuel pumped to it with the eng feed knob in off - setting it to norm turns on the electric pumps, but there are also pumps running off engine bleed air at all times regardless of the knob position. So you get the siphoning system, electric fuel pumps, and bleed air driven pumps… I somehow suspect someone put a bit of thought into the engine design there.
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Although, the wire should not prevent you from rapidly moving it as required.
Little off topic, but that’s why it’s not “safety wired”, instead of using safety wire (metal, used to secure nuts and bolts), break wire is used. To make sure the operator does not change the switch accidently, he will have to use some additional force to change the switch position if he want’s to. And like you said, the wire should not prevent movement.
(I know, just details, but as a technician, hearing somebody say to safety wire a switch gives me the shivers
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Well its not going to indicate perfectly like it does in BMS, not during maneuvering flight…
USAF regs have minimum fuel level permissible for landing as being 1000 lbs - I vaguely recall reading somewhere that the 8 FW regulated bingo was 2400 lbs? IIRC that was so you could make it to Osan in case there was an emergency and the ALS could not be set up in time, and still have more than emergency fuel over Osan.
Back on the topic of the DEC getting adequate cooling, it still gets fuel pumped to it with the eng feed knob in off - setting it to norm turns on the electric pumps, but there are also pumps running off engine bleed air at all times regardless of the knob position. So you get the siphoning system, electric fuel pumps, and bleed air driven pumps… I somehow suspect someone put a bit of thought into the engine design there.
…heh…yeah, I did…back when I had that job at GE. It’s not just about the DEC…there are a number of things hanging on the engine that the fuel flows through/past that contribute or could cavitate if they run dry. 1000 lbs on-deck is certainly reasonable, though I can agree that the RTB considerations you mention can also be factored in per location requirement. I couple of jets I’ve operated have hard on-deck fuel requirements which are primarily aimed at engine/system health - the “health” min for the Viper is probably something around the low fuel warning in that regard. When I was operating Harriers the guys used to take pride in the low fuel light coming on as the jet was chocked…that’s 200 lbs for that jet, which also has a DEEC.
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DEC should be the only fuel cooled bit on there. The engine schematics show the three items on the fuel cooling loop being the DEC, the pyrometer, and cooling fuel shutoff valve. There’s a bunch of fuel operated stuff on there - like half the systems at least seem to be hydromechanical and most of the rest being electrohydromechanical… using fuel pressure to run things is a neat concept.
And on the topic of pressure, all the fuel operated (but not fuel cooled) systems get additional pressure from the engine fuel boost pump as well, regardless of the eng feed knob position.
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…like I said…there’s more to it than just cooling the DEC. From an engine standpoint. Yes, the working hyd fluid in the engine is fuel (and in some cases it and/or oil are also used for heat exchange or pre-heating)…and keeping it circulating and at proper pressures can also incur mechanical consequences. When new engines are shipped they are not shipped “dry”. And in some cases motoring the engine to “prime” it is required post-maintenance - depending on what was done - before actually running it up. But that’s a really short evolution.
One of the things I was really surprised by is the discussion elsewhere of “Viper wine” due to the Pratt nozzles being electrically actuated…I’m not really sure I believe that. But I wouldn’t put that past Pratt.
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PW220 and PW229 nozzles are actuated by high pressure bleed air.
It looks like we agree that running the engine dry is probably bad for it. I think we agree it is working optimistically in BMS at present during flight with either reservoir less than full? I mean, if you have the eng feed knob off, and a reservoir less than full, then any negative G could starve the engine of fuel. Which would be bad.
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…bleed air? That’s even worse, IMO…ever seen the damage a bleed air leak can do?
Yeah - I was thinking mostly about ground ops, though. That’s probably where a mistake is most likely to happen. Unless you secure the feed knob airborne for some reason - I can’t think of one…other than in flight fire, maybe?..
There are a LOT of things working optimistically in BMS…which surprises me. A bit. Probably my own fault - I think I’ve over-hyped it to myself before actually working with it extensively. BMS still rocks, though.
Stevie
