Grounding 737S Could Cause Engine Failures

[straitman]

Here is a part article from World of Aviation. I expect that we will hear a lot more about this.

GROUNDING 737S COULD CAUSE ENGINE FAILURE, WARNS FAA
written by Hannah Dowling July 27, 2020


The US Federal Aviation Administration (FAA) has issued an emergency airworthiness directive for Boeing 737 aircraft, warning of potential corrosion issues on planes that have been parked amid the COVID-19 pandemic, which could lead to a dual engine failure.

The directive was issued for more than 2,000 Boeing 737 “Next Generation” and “Classic” aircraft registered in the US, including all Boeing 737-300, -400, -500, -600, -700, -700C, -800, -900 and -900ER series aeroplanes.

Following “four recent reports” of single-engine shutdowns on 737 aircraft, investigators reportedly found that the plane’s “engine bleed air fifth stage check” valves had the tendency to stick in the open position.

“If this valve opens normally at take-off power, it may become stuck in the open position during flight and fail to close when power is reduced at top of descent, resulting in an unrecoverable compressor stall and the inability to restart the engine,” the FAA said.

This fault was reported to be as a result of corrosion, caused by the plane remaining grounded for a period of seven or more straight days.

The airworthiness directive also noted that corrosion of this kind on the valves of both engines could result in a “dual-engine power loss without the ability to restart”.

 

[eric2011]

Oh thanks alot...makes me feel good about my "800" flight to TSV tomorrow

 

[tgh]

America : where on a quiet night you can hear the Fords and the Boeings rusting….

 

[jb747]

So, they should be engine running them whilst not flying. I'd actually have expected them to be doing so, but I guess not....

I suspect there will be a whole rash of 'new' issues when they eventually try to get aircraft back into the air. It's one of the reasons I don't see the A380s returning.

 

[eric2011]

So, they should be engine running them whilst not flying. I'd actually have expected them to be doing so, but I guess not....

I suspect there will be a whole rash of 'new' issues when they eventually try to get aircraft back into the air. It's one of the reasons I don't see the A380s returning.

Would this issue occur at any time or just on the first time out after a long period

 

[Fergo747]

I suspect there will be a whole rash of 'new' issues when they eventually try to get aircraft back into the air. It's one of the reasons I don't see the A380s returning.

Would you be able to elaborate on this point a bit further? I'm curious based on your intimate knowledge of the A380 what you perceive could be a 'new' issue that would not warrant rectification and then resumption of flying for this type (putting aside for the moment the fact that there is unlikely going to be demand for an aircraft of such capacity in the short to medium term).

From an aircraft agnostic perspective, what other issues do you foresee in getting the aircraft back up and running (assuming proper maintenance is being carried out whilst in storage)?

 

[straitman]

Would this issue occur at any time or just on the first time out after a long period

Ongoing. Otherwise the engine could simply be run up and down a few times I resolve the problem and the AD would be written to incorporate that.

 

[jb747]

Once the valve has been damaged, the only alternative would be to replace it. The damage could be avoided by exercising the valve regularly. Just how regularly is the question.

Engines produce massively varying amounts of bleed air. At idle, very little, so it's taken from a high pressure section of the engine. At high power it comes from a low pressure section. It changes many times during a flight. You can often feel, and hear, the change just after top of descent, as the engines go to idle, and the bleed switches from low to high stage. An engine operating in the wrong 'stage' can disrupt the airflow through the engine (hence the shutdowns). It can also do damage to the bleed ducting, and potentially even the pylons.

 

[jb747]

Would you be able to elaborate on this point a bit further? I'm curious based on your intimate knowledge of the A380 what you perceive could be a 'new' issue that would not warrant rectification and then resumption of flying for this type (putting aside for the moment the fact that there is unlikely going to be demand for an aircraft of such capacity in the short to medium term).

From an aircraft agnostic perspective, what other issues do you foresee in getting the aircraft back up and running (assuming proper maintenance is being carried out whilst in storage)?

All of the aircraft in storage will be suffering from issues with the myriad systems that have not been exercised during the storage. Proper maintenance would really include flying them, and that simply isn't going to happen. The 380 was already an aircraft that was prone to all sorts of glitches, and this simply gives an opportunity for them to accumulate. It simply won't be worthwhile sorting them out by the time they're needed again. If that time ever actually arrives.

 

[RAM]

That announcement is a little surprising after reading the Hawaiian Airways piece a few months back about the maintenance requirements for their parked planes to keep FAA airworthiness.

There were daily, 2 daily, .. weekly..monthly requirements for maintenance work. I'm sure one was engine start every 2nd day but memory could be out slightly - definitely was more than weekly. This fed into their explanation about how their planes were parked.

JB747 may well know more specific info as to whether the FAA has more airframe specific maintenance requirements (A330, A320, B737-800 etc).

 

[jb747]

There were daily, 2 daily, .. weekly..monthly requirements for maintenance work. I'm sure one was engine start every 2nd day but memory could be out slightly - definitely was more than weekly. This fed into their explanation about how their planes were parked.

JB747 may well know more specific info as to whether the FAA has more airframe specific maintenance requirements (A330, A320, B737-800 etc).

I think that what is happening is that they are finding new sources of failure, in systems that they hadn’t previously been concerned about.

The sort of engine run that I’m talking about is a full power run, and that would mean towing the aircraft to an appropriate bay. As most are literally parked in, that‘s probably impossible.

My knowledge of the maintenance procedures is very limited. I’d expect though, that every aircraft type has it’s own set of requirements. They’d be from the maker, not the FAA.

 

[ja1]

Interesting to know the process involved with valve replacement (full engine rebuild?) and whether that means they would be replaced with a newer design that won't have this specific issue.

Also interesting to think about whether an exercise procedure will be developed to specifically deal with this valve (and others) that doesn't involve a full engine runup.

It did beg the question.. (and only thinking about this because I had a chance to visit a USAF base and noticed there was a large lot of jet engines sitting in storage..) about taking all the engines off the parked aircraft and putting them into a specifically designed storage facility..

A lot of those aircraft that are parked aren't going to be flying for 12/24/36 months (or ever again in the A380s case)..

 

[jb747]

Interesting to know the process involved with valve replacement (full engine rebuild?) and whether that means they would be replaced with a newer design that won't have this specific issue.

I’m pretty sure that it can be replaced with the engine mounted. There won’t be another design just to counter this, unless you’re planning on more multi year groundings.

Also interesting to think about whether an exercise procedure will be developed to specifically deal with this valve (and others) that doesn't involve a full engine runup.

Which is how Boeing got themselves in this mess to start with. Not testing completely and in situ. Same issue with their Starliner capsule.

It did beg the question.. (and only thinking about this because I had a chance to visit a USAF base and noticed there was a large lot of jet engines sitting in storage..) about taking all the engines off the parked aircraft and putting them into a specifically designed storage facility..

A lot of those aircraft that are parked aren't going to be flying for 12/24/36 months (or ever again in the A380s case)..

If you remove the engine for any lengthy period, a mass should be installed in its place, otherwise the wings eventually distort.