DC-9 ground collision injures 6
Halfnut: The transfer pump you refer to must be the alternate pump. My"source" claims that it is the only connection between the two systems and that the left can operate, via the gear sump fluid (but with no right pressure indicated) the landing gear, right half of the nosewheel steering. From the right to the left, the left at reduced pressure (18--2400 psi), if the normal fluid in the right side is available over 2,000 psi., to go through priority valve (normally 1500 in cruise or 3,000 during approach, taxiing and until Climb Checklist, following "uplatch check"), to get to the non-priority items. A problem with whichever DC bus (rare) might affect the anti-skid, if left on after landing and the right DC Bus powers the alternate hydr. pump. Doubt that they also had such an electrical abnormal, or had a groundshift failure. The Aux pump powered by Left Gen. Bus, based on my information. Better go now. Don't want to look too sleepy in Sun. School. 
...eing'schlohfe...
...eing'schlohfe...
Last edited by Ignition Override; 16th May 2005 at 05:08.
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Gosh Ignition Override I didn’t know I was going to get an oral on the DC-9 hydraulic system. Yes your source is correct on the exact numbers and wiring on the DC-9. The Transfer Pump will transfer pressure but not liquid. Depending on which side has more pressure will make one side a motor and the other side the pump there by pressurizing the other side. It does it in pulses and if you sit over the wing on the ground with one side unpressurized you can hear the Transfer pump making a thumping noise under your feet. But getting down to the brass tacks it is enough power to keep your brake system charged so you can stop the aircraft.
I’ve been told too that the Transfer Pump is the only place where the two systems come together. Ask your “source” if there are any hydraulic fuses or check valves on the brake accumulators to maintain brake pressure in the event of a complete loss of hydraulic fluid on either side?
I’ve been told too that the Transfer Pump is the only place where the two systems come together. Ask your “source” if there are any hydraulic fuses or check valves on the brake accumulators to maintain brake pressure in the event of a complete loss of hydraulic fluid on either side?
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- The transfer pump has had various names (Power Transfer Unit - Alternate Pump etc.) on various DC 9 / MD models. There have certainly been cases of case cracking with this unit, which can lead to loss of fluid. Once one side is fluid free and thus free rotating the other side soaks up pressure from the live system in the attempt to maintain pressure on the dead side. This results in an almost total hydraulic failure. The problem was known over seven years back and certainly occured in an airline I worked for.
- This engine shut down business - I once worked out how little fuel you saved - especially considering increased thrust on the live engine when making turns towards it. Maybe someone will re-consider whether making it an SOP is such a bright idea - especially when the Pratt should be given a cool down period after landing.
Add some system failure - electrical or hydraulic and you could be compounding the problem.
FC.
- This engine shut down business - I once worked out how little fuel you saved - especially considering increased thrust on the live engine when making turns towards it. Maybe someone will re-consider whether making it an SOP is such a bright idea - especially when the Pratt should be given a cool down period after landing.
Add some system failure - electrical or hydraulic and you could be compounding the problem.
FC.
Few,
Perhaps what you describe explains the feature of the MD80 that automatically closes two shutoff valves if either reservoir fluid level drops below "...a safe level..." ( actual quantity unspecificed in our manual ), rendering the transfer pump inop.
I flew the -30 for a very long time and was never told of the condition you describe with the alt pump in a fluid loss condition. But that's what keeps it so interesting...learn something new all the time.
The Douglas DC9 manual contains the following statement re the alt pump: "The input pressure from either left or right hydraulic system is controlled so that not more than 2 gallons per minute flow will be used to drive the hydraulic motor/pump." Further, the DAC manual says that the engine driven and aux electric pumps are capable of 8 gpm @ 3000psi.
Perhaps this feature malfunctioned in the cases you experienced. At any rate, always fun to have some "shoptalk" with fellow DC9 pilots.
Perhaps what you describe explains the feature of the MD80 that automatically closes two shutoff valves if either reservoir fluid level drops below "...a safe level..." ( actual quantity unspecificed in our manual ), rendering the transfer pump inop.
I flew the -30 for a very long time and was never told of the condition you describe with the alt pump in a fluid loss condition. But that's what keeps it so interesting...learn something new all the time.
The Douglas DC9 manual contains the following statement re the alt pump: "The input pressure from either left or right hydraulic system is controlled so that not more than 2 gallons per minute flow will be used to drive the hydraulic motor/pump." Further, the DAC manual says that the engine driven and aux electric pumps are capable of 8 gpm @ 3000psi.
Perhaps this feature malfunctioned in the cases you experienced. At any rate, always fun to have some "shoptalk" with fellow DC9 pilots.
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Bafanguy,
It´s been a while but MDC had the pump casing modified as I recall.
The condition didn´t occur with a straight loss of fluid but only when there was a crack in the casing of the pump. (Of course the pump normally won´t run unless there is a pressure drop on on side and a crack in the casing tended to create a very sudden loss.) Could well be that the system on the good side recovers when the cut off level is reached- but the incident may have happened by then.
A similar pump was used by the way on the DC-10 between the systems, where it was called the motor pump - typical Douglas - a new name for an old system every model.
I once had access to all the literature on this but am working from memory now.
All the best,
FC.
It´s been a while but MDC had the pump casing modified as I recall.
The condition didn´t occur with a straight loss of fluid but only when there was a crack in the casing of the pump. (Of course the pump normally won´t run unless there is a pressure drop on on side and a crack in the casing tended to create a very sudden loss.) Could well be that the system on the good side recovers when the cut off level is reached- but the incident may have happened by then.
A similar pump was used by the way on the DC-10 between the systems, where it was called the motor pump - typical Douglas - a new name for an old system every model.
I once had access to all the literature on this but am working from memory now.
All the best,
FC.
It'd be very interesting to learn how the two aircraft were extricated from this embrace, the DC-9's port wing and fuselage under and lifting the 320's fuselage. It must have been a very delicate operation, not to compound the damage; where do you put any airbags under the 320 if the DC-9's wing is nearly up against the 320's main gear? You can't pull the DC-9 out then, can you. Lift the 320's wing between root and stbd gear? Gosh, with people watching from the balcony, a job to get done very quickly. Also interesting, somewhere down the road, to learn whether either aircraft get back into service, how long it takes. The 9 might just be scrapped but the 320?
My apologies to the DC-9 captain for a flippant post earlier on re haircuts. Obviously a lot more potential for damage inside than I'd originally realised from the first photos posted. I do hope it's not too much more than a dust yourself off thing.
My apologies to the DC-9 captain for a flippant post earlier on re haircuts. Obviously a lot more potential for damage inside than I'd originally realised from the first photos posted. I do hope it's not too much more than a dust yourself off thing.
