B767 bleed fault (HPSOV)

[cod liver oil]

Crew reports EICAS “L ENG HPSOV” + BLEED light illum during descent.

FIM tells me that this message will present itself whenever HPSOV is not closed when it has been commanded to close.

Question: Why would this message appear on descent? Shouldn’t HPSOV be open with engines at flight idle on descent?

(CF6-80C2 engines)

Tia for your replies

cod

[cod liver oil]

You are correct Fargoo … when >127psi detected at High Pressure Controller, servo pressure from HPC is vented to ambient resulting in HPSOV being commanded closed. If HPSOV does not close, EICAS msg appears + Bleed lite.

I understand the system logic ... I'm just wondering why would I have 127+ psi (overpressure as you term it) from 14th stage HP bleed when engines are at low power setting on descent?

(BTW, I didn’t fix it … aircraft was released per MEL 36-11-02)

[grounded27]

I would suspect it is a bad PIREP, we see this all the time at TOD as you had said when throttles are retarded.

[kingstonboy]

From experience (b767,b747)number of issues with ata 36, never dismiss HP valve failure, try lubricating and exercising the vlv position switch arm(sometimes the problem is very obvious)
Controller and sense lines also prevalent(beware of unions that `weld`together) another favorite is the wiring ,chaffes are very common. The Earth line is also problematic ,ask your Tech services can you try a local earth.
The usual T/Shooting (in reality)goes along the lines of vlv,controller and then wiring.
Another good tip review cmc /ahm the snapshots can sometimes be enlightening.
As has already been discussed eng at low power settings the risk of overpx highly unlikely.

[aveng]

Doesn't the HPSOV open again at idle thrust to augment the IP air. If the crew nudge the throttles slightly and the light goes out - its a case of HPSOV still closed when commanded open.

[cod liver oil]

I think you are right about possible culprits kingstonboy (valve, controller, or wiring) ... bleed card could be at fault too.

We operate -300's Fargoo ... no CMC ... equipped with air supply bite module.

Thanks all for the replies

cod

[Piper19]

Aveng, the message only appears if the valve is open with closed command, according to the FIM, that's why it's strange to have on descent.
Things I would do before MEL-ing is check all the sense lines and check the controller/bleed cards

[Beeline]

Piper 19 how long are your turnarounds?

Valve, Controller, sense lines, icing. Could be anything or all of the above that's why we engineer our way to the solution.

You could also check the dodgy earth to the EICAS computer that brings it on in the decent as opposed to TOD. Lol

I was always taught look at the obvious and take what is written in the log as the failure and not a technical description!

[cod liver oil]

Alright, with a few posts mentioning sense lines, it begs the question … Why?

If the sense/servo line pressure is lost, this would affect HPSOV ability to open.

According to FIM, the message is appearing because HPSOV is not closed when it has been commanded to close.

Doesn’t this rule out sense lines, or am I missing something here?

[Beeline]

If the servo muscle air cannot be ported to ambient it will keep the valve open.

Most/all HPSOVs spring loaded to fail safe closed. Have known blocked vent ports to cause this issue especially on handling bleed valves.

[cedgz]

i should run the engines and check the bleed syst(especially the hp closure at certain psi/eng rpm and reopen)
if all ok, release the airplane, and monitor further pipers
as mentionned above, hp should be open in descent(except if they throttle up)
signoff would be" adj/test satif rem mm 36-bla-bla-bla and if problem reoccurs plz report throttle setting and bleed press and other parameters such as anti-ice"

[Beeline]

Last poster, is this on a turnaround?

Can I ask how you get the engine past idle to an adequate power setting for HP/IP change over on stand?

The OP was on the technical aspect of the snag post an MEL dispatch, that if time was not available the complete way to go about things. Lock the bloody thing out send it on its way.

Please post a reasonable technical evaluation of the problem not how you would flog it on, I'm sure we can all post that sort of content.

[rmm]

What did the AS BITE show? You could also ask the crew to take a snapshot of the pneumatic page when it happens then compare the duct pressure readings of both engines. I've seen this message before with normal duct pressure on both engines. Turned out to be a wiring/indication problem

[cedgz]

"FIM tells me that this message will present itself whenever HPSOV is not closed when it has been commanded to close."

Beeline: "If the servo muscle air cannot be ported to ambient it will keep the valve open."

Your statement is technically right, but it doesn't answer the problem, on descent hp should be open(idle) and he receives an eicas msg that per fim means hpsov is not closed.

So if time permits i would run the eng on a remote stand, and start troubleshooting from the results i found(real hpsov failure or indic failure) or lock the vlv out per mel.

This snag is just as AP inop(no flightphase,mode, etc) and means nothing

So even before starting looking at muscle press lines, smooth vlv movement, etc, you might run at the stand on idle first and make an idea about this.
At least you know for sure wich vlv to properly lock out for mel(hpsov or prsov)

[Beeline]

Please explain how you isolate the PRSOV as the source of failure when you are not allowed to run the engine above idle??

Selecting the bleed off will close both HPSOV and PRSOV and doesn't troubleshoot anything bar the HPSOV closure function.

This can confirm a fault but only at switch level not at crossover where the fault could lie as at TOD.

Maybe the aircraft was commanding the valve closed but couldn't, it could be many a problem but untill you contact the aircraft no one will ever know!!!

Beeline out