737-800 Eng bleed tripoff as T/O
 

Last month a company had happened a strange incident, the crew was using no engine bleeds air to takeoff in a high elevation airport, as rolling right eng bleed tripoff light illumninated, the crew dicided to go on flying, as flying to the safe altitude, they were trying to do the normal procedure to recover the bleed air, as soon as the right eng bleed air switch was turned on, the pressurization sys changed to alternate one, and the cabin altitude went higher than normal, as passing 10000ft, the cabin warning horn was on........finally they flew the plane back,

I an wondering if anyone had got this before, and boeing seems to have issued some fob about this but I can not find this, could anyone help me to find so? thx a lot for any feedback.

Certainly the bleed trip is by no means uncommon and I think caused by the temp switch upstream of the bleeds valve. The press'n. problem I have not seen - but have not operated 'high'.

Eng bleeds off t/off and they got a R Eng bleed trip. Is that correct? Anything else?
What altitude was the strip? OAT?

Pressurisation problem could be caused by large rate of change in pressure (in or out) sensed by controller as a failure.Just a hunch.

Like to see how the defect was dealt with.

Lets start with the pressurisation auto fail - a bit of a red herring I think.

As the above poster has pointed out, this may have been a function of cabin alt rate too high or cabin alt to high. The CPC is designed to swap for any of these occurences, and is not really a system failure in the above case, but rather 'user error'

The CPC BITE will show the reason it failed itself.

Bleed Trip is caused by either a high pressure (220psi) or high temp (490F). Bleed snags on the NG are notoriously difficult to identify, and Boeing have issued numerous service documents to assist maintenance in identifying the causes.

In this instance my money would be on a high pressure bleed trip, caused by the high stage valve that has failed to close fully.

GR - I am working on what a 'spanner' told me, but he said the temp sensor is upstream of the valve, the pressure downstream. Normally we check zero px in the duct so I don't think it would be a px trip? Certainly these trips were common enough for me to include the 'actions' if it went during the take-off roll (which is normally did).

http://www.thegoldenrivet.com/photog...s/NG_Bleed.JPG

You need to invest in a new 'spanner'.....

The 390 temp sensor, 450 temp sensor and 490 temp switch are all downstream of the PRSOV.

The overpressure switch (housed within the bleed air regulator) monitors pressure upstream of the PRSOV.

.

I suspect the 'spanner' is about as old as me, so it was a while ago - I obviously got the two 'reliefs' mixed up, but whatever the limiter, the trips happened.

When I find that spanner.................................:)

The 733 has a similar if not identical Bleed system.
 

On the 733 it was common to see a Bleed trip off on a Bleeds off Take-Off.
If a reset was not successful, selecting the respective Engine Anti-ice on before attempting a second reset would usually allow it to reset (reopen).

The EAI is taken upstream, before the PRSOV, this allows the bleed air to flow, releaving an overpressure and avoiding an overpressure during the reset.

that's really interesting, is it a boeing suggestion? but seems nice. thx

Eng bleeds off t/off and they got a R Eng bleed trip. Is that correct? Anything else?
What altitude was the strip? OAT?

Pressurisation problem could be caused by large rate of change in pressure (in or out) sensed by controller as a failure.Just a hunch.

Like to see how the defect was dealt with.


I can not handle the quote staff , sorry~~~
that's right R Eng bleeds off at first and can not be reset. At the altitude about 12000 the cabin rate become crazy, which trigger the warning horn. furthermore, the PM was too nervous to act well , he put the PAX Oxy mask on, ......... finally they came back normally, that's lucky.

Sorry cavadina can't remember if it came from Boeing, it's quite a while since I was on the 733 and never had the necessity to do a bleeds off on the 738. Check the EAI MEL, from memory it has a limit of 38ºC.

That's ok, I will try to look through my mannual to find out the solution,

I can confirm the anti-ice 'fix' but not its origin, and of course don't tell anyone.........

Cavadina, get maintenance to replace high stage valve.

cavadina,
thanks for that. I agree with golden rivet re hi stage valve (it is a guess not actually being there].
The bleed air regulator gives plenty of trouble at our airline too.

the new gen 737 is a great aircraft but the bleeds are still a problem.

Yes, I agree, the 737ng is a awesome staff, but the pressuization and a/c sys seem not as well as the 757 or the other ones,

This subject is addressed by FCOM Bulletin TBCE-5 dated June 16 1995, Title: BLEED TRIP OFF light illuminated during a no engine bleed takeoff.

I cant copy it all here but its operating instructions instructs you to put engine anti-ice on on the affected side if a normal reset is not possible and then reset again.

S&L

Edit to add that this bulletin was for Classics only.

As CaptainSandL pointed out, the bleed air reset with EAI On proc detailed in a Boeing issued FCOM bulletin to rectify a Bleed trip during a No-Bleeds T/O caused by the incapacity of the High pressure relief valve to vent sufficient pressure at t/o with bleeds off. Noteworthy is that Boeing only issued it for the Classic as the NG has a redesigned high stage relief valve.

An interesting read on this topic is the recent depressurisation of VH-VBC, a
Boeing 738 at Coolangata Australia. The report is available at the ATSB website.

Cheers,
MHA

High pressure relief valve.... :confused:

Wheres that fitted then ?