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Guest nihongo

Crossfeed, Engine Out and such as HOW???

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I own the PSS 757 with the manual, but it doesn't describe the systems in detail. With the fuel system, how can you crossfeed so I rectify desceprency in my left and right wing tanks?With an engine out, what is the procedure for a restart (you have to lower your FL) and obviously DO NOT NEED BLEED AIR!Just a couple of curious questions, does anyone have knowledge os this?

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Hi I dont have the 757, but the procedure will be to open the xfeed valve and switch off the pumps in the tank which has least fuel. Both engines will then take fuel from the fuller tank.I dont know the procedure for your second question, but would think that you surely do need bleed air to get the n2 speed up to the required level ?Let us know how you get on.Peter

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Peter,Thanks, that is what I thought (because I don't understand the fuel system, I thought you need a left and a right pump to keep left and right engines going?), Maybe time to get my hands on a real Boeing manual. Not too hard for me.But about the engine start, the airspeed would be enough pressure to try a relight at around FL150?I will check with Captain Lim (T7 Captain).Danielf111RAAF.blogspot.com

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You can usually restart an engine at any speed using an assisted start. It is only on the windmillling airstart where you need to have a certain airspeed to relight. Crossbleed air from the other engine or APU is used for the assisted starts.During fuel crossfeeding, the single pump supplies its engine and the other via the crossfeed line.

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Back in the mid 80's I was riding along on a freight flight in a Lear 23 when we lost an engine while climbing through FL33.Before trying a air restart the manual said we had to get down to FL25. I think because of air density which might be common to all turbines just to get the burn started. We tried both a restart with it wind milling at 30% and a starter assist which popped the circuit breaker. Both failed because the high pressure engine driven fuel pump had a sheared shaft. An FAA AD note after that was issued.

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>Peter,>>Thanks, that is what I thought (because I don't understand the>fuel system, I thought you need a left and a right pump to>keep left and right engines going?)>>DanielYou will find that the engines will run just fine with no pumps on. The system is designed to draw fuel through suction in the event of loss of all pumps in any tank.To equalise tank levels , the pressure from pumps in one tank only, feeding through the cross feed manifold is sufficient for both engines. Peter

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Interesting incident! Did you complete the flight or divert?What does the AD mean? (AD stands for?)

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Thanks Peter. That gives me an idea how the system works. Is this for all Boeing system aircraft?Did you see the Air Crash Investigation episode on the aircraft that had a fuel leak, and the Captain was transferring fuel across to the leaky tank?Daniel

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We were en route from Fulton County airport in Georgia to Pontiac Michigan. We landed in Lexington Kentucky because we hadn't ruled out bad fuel from the refueling truck and were thinking the other engine could flame out. After a successful landing we disconnected the fuel line at the pump and checked for contamination but it was ok. The company sent down an Aero Commander 690B to pick up the load we were carrying at 2:00 am and I rode back with him leaving the crew with the Lear.AD = Airworthiness Directive. AD notes are issued by the FAA and end up being very expensive. The notes can be limited to range of serial numbers for any components, engines or airframes. They can be as simple as remove and inspect to remove from service. In this case the engine driven high pressure fuel pump runs from a shaft that is connected to the main turbine shaft. As with many accessories that run from a shaft, those shafts have a shear point with lessor diameters that are meant to shear if the accessory fails and jams. If the accessory is not jammed, the shear point must be suspect, either metallurgy or the manufacturing process, because engineering is never wrong ;>).Lessons to be learned : When your shift ends go home, never accept a short flight down south and be back home by 11:00 pm. ;>)

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Good point.But these days I think the US has FAA and FRA (Fed. Railroad Admin.) maximum shift lengths. I understand with rail that once the twelfth hour is reached the train is stopped. That is a permanent stop until a fresh crew can relieve the max shift crew. So despatch puts it in a siding. No can do with Flying metal though!

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