Now Another Aircraft Type Grounded

[PeterRS]

After the engine explosion on the United flight from Denver, 69 Boeing 777s in the USA and Japan using that same engine type have now been grounded. But Boeing has recommended grounding more than 120 aircraft worldwide. Japan has also banned all such aircraft from overflying its airspace.

If memory serves me correctly, the arrival of the 777 in the 1990s and the rapid extension of the rules permitting twin engine aircraft to fly over water for more hours were a direct result of more powerful and safer engines. United 328 to Honolulu was only minutes after take-off when one engine failed. With the engine continuously on fire, the captain of the United flight was able to quickly turn around and land safely back at Denver. What I wonder would have happened if the engine had failed and continued on fire half way between the west coast and Hawaii? That's a flight time of about 5 hours over water with no intermediate airport. Would the continuing fire then have started to melt part of the 777's wings?

The 777 has an enviable safety record. But this was a failure of an engine produced by one of several engine suppliers. As has happened before, regulators were aware of potential problems with this Pratt and Whitney engine type. Yet little seems to have been done to correct the problem. 

With the much bigger engines nowadays, we have already seen the sort of damage that can be done in a sudden failure when Qantas pilots managed to get their A380 en route to Sydney safely back to Singapore even with most of their control systems out of action and damage to the fuselage. But that again took place less than 5 minutes after take off from Singapore and depended on the fact that there were two cabin crews on board. What would have been the result if it had been mid-way over the Indian Ocean on its previous leg?

I am starting to miss the tried and true Lockheed L1011 Tristar.

[Guest]

1 hour ago, PeterRS said:

 I am starting to miss the tried and true Lockheed L1011 Tristar.

I also prefer 3 or 4 engines.   Apparently, 4 engines are a requirement for Air Force One, yet replace one old man with hundreds of paying passengers and 2 engines are sufficient.

However, the TriStar managed 540 fatalities from a production run of 249 aircraft.

The 777 has had 541 fatalities from 1656 aircfaft and the passenger capacity is higher on a 777.  So over 6x better than a L1011, although presumably the 777 fleet has a longer life ahead of it.

Despite high profile incidents, this is still by far the safest era in which to fly.

[fedssocr]

Apparently the aircraft that UA rounded up to fly the passengers on to Hawaii had itself suffered a similar engine failure a few years ago on a flight from SFO to Hawaii. That time they returned safely to SFO.

777 ETOPS is 180 mins, I believe, on one engine. If they were over the ocean they would either turn around and go back to the West coast or continue to the closest diversion airport.

4 engines are a lot less fuel efficient. And the 777 has performed extremely well over the years as noted. Sounds like the problem with these PW engines is their hollow fins.

[Guest]

From my limited understanding of the issue, hollow fins have been standard in large gas turbine engines for decades.

From basic thermodynamics, the higher the combustion temperature, the higher the efficiency.  They actually run at temperatures far beyond the safe limits of the alloys, but a thin layer of cooler air protects the blade.  That air is fed through the hollow blade.

If you think that's risky, remember the alternative is higher fuel consumption, reduced range, worse global warming and higher ticket prices.

As for safe time over water, this isn't an issue flying from the UK to Thailand.  However, we do fly over some choice places, like Pakistan and Afghanistan. I wouldn't really fancy an unscheduled stop in Kabul.

They started detouring around the Ukraine, after the Russians shot down a Malaysian plane.

[PeterRS]

Interesting article on the CNN website this morning regarding the problems Boeing is now facing. The 777 has proved a profitable and reliable aircraft for the company. But some existing 777s are proving unpopular with airlines. Last year Delta announced it would retire all 18 of its 777s even though 8 had been in service for only 10 years. Then Boeing's latest longer range model the 777X has been affected by serious delays in getting the first production model off the ground.

Like all twin engine jets, production of the 787 Dreamliner is being affected by very slack demand due to the pandemic and the resultant major reduction on international routes. As a result, one of the two plants that build the aircraft will be closed down. Worse, late last year Boeing halted deliveries due to problems with the 787 horizontal stabiliser. Then last Friday the FAA ordered inspections of more than 200 already delivered 787s due to torn decompression panels in the cargo holds. The FAA considers this could result in a risk of fire. Not very encouraging for those thinking of flying the 787.

https://edition.cnn.com/2021/02/22/business/boeing-widebody-jet-woes/index.html

[anddy]

 

13 hours ago, z909 said:

From my limited understanding of the issue, hollow fins have been standard in large gas turbine engines for decades.

From basic thermodynamics, the higher the combustion temperature, the higher the efficiency.  They actually run at temperatures far beyond the safe limits of the alloys, but a thin layer of cooler air protects the blade.  That air is fed through the hollow blade.

Not sure how this relates to the engine, or rather blade failure in the most recent incident. That (hollow) blade has nothing to do with combustion, as it was from the large fan at the front of the engine, as can be seen in the image. According to the BBC article it was simply "metal fatigue"

 

[Guest]

10 hours ago, anddy said:

incident. That (hollow) blade has nothing to do with combustion, as it was from the large fan at the front of the engine, as can be seen in the image. According to the BBC article it was simply "metal fatigue"

 

 

Agreed, in this case the hollow blade is nothing to do with combustion.
The metal fatigue explanation is a bit simplistic.  Of course it's likely to be fatigue, since it's not failed on the first load cycle and it's presumably not exceeded the normal rotation speed.
However, these blades will have a carefully calculated design life, during which failures should not occur.  So there is some other factor, such as a manufacturing defect, subsequent damage, exceeding permitted operating hours (unlikely) or an error in the life calculations.
I expect Pratt & Whitney can establish the crack initiation point from examining the fracture surface.   Then check for abnormalities.  They are probably re-examining the stress calculations for this part as well.   They can probably establish the cause quickly, unless it's some obscure issue like an unexpected vibration mode.