MSNBC is doing a documentary on "Miracle on the Hudson", the incident of the airliner . . .

[brush]

landing in the Hudson river.

I had forgotten it was forced to land on the water because of a bird strike that incapacitated the jet engines.

What I don't get is why they don't put some sort of screen over the openings of the jet engines that would let air in but keep birds out.

Anyone have any expertise on this?

[NutmegYankee]

1. Screen disrupts airflow and allows ice formation.

The high altitudes can allow ice to coat the screen, choking the engines. A screen, one that can survive a brutal high speed collision, would also rob performance as it messed up the intake airflow.

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3. Couldn't the screen, or maybe a wire mesh have, de-iceing capability?

Slightly lessened performance from the drag of the mesh would seem to be better than being vulnerable to bird strikes.

[NutmegYankee]

4. You realize a simple wire mesh would be tissue paper at 200 mph right?

Bird strikes on an engine are rare. The problems of blocking the engine intake are far worse.

Also, it isn't slightly worsened performance - it's substantial.

[brush]

8. Ok, not a mesh but a grid spaced enough to keep birds out but not collect debris?

Just curious why the problem of bird strikes can't be solved.

[NutmegYankee]

10. The tradeoffs are not worth it.

I could make cars that would be able to hit a tree at 100 MPH and not harm the passengers, but the trade off would be incredible weight and 3 MPH fuel economy. That would cause side impacts like increased road damage. It's not worth it.

[The Velveteen Ocelot]

6. De-icing/anti-icing would require the use of hot air from the engine

which would further decrease its efficiency; and if so the screen would have to consist of hollow tubes. Some anti-ice systems use electrical power but the surface of such a screen would probably be too large for efficient electrical de-icing. Anything like this would increase the complexity of the engine, add to the weight, and decrease its efficiency. The engines already have hot-air anti-icing on the hub which keeps the Pt2 probe open and keeps ice from being ingested into the engine. Which raises another problem: if the screen collected a lot of ice and that melted off, water would be sucked into the engine. If enough water got into the engine it could flame out (this can happen in very heavy rain or hail).

[brush]

17. Thanks. Just thought there could be a solution to bird strikes.

[The Velveteen Ocelot]

2. Several reasons.

One reason is that there is a thing called a Pt2 probe right on the hub of the 1st stage compressor section. That sensor detects the air pressure at the intake of the engine, and that pressure is compared to the pressure at the exhaust section. This ratio is called the engine pressure ratio (EPR), which is read on a cockpit instrument and is a way of determining engine power production. If there was a screen over the engine inlet, that screen would quickly collect debris (the engine sucks a lot of air) and would result in an inaccurate reading at the Pt2 probe, and therefore inaccurate EPR. Furthermore the debris would eventually reduce the total air intake into the engine and it would not run properly and might quickly overheat.

[brush]

5. It would require rethinking but ouldn't a grid with wires spaced enough to keep birds . . .

be designed not to collect debris but be engineered to not interfere with the functions and critical measurements you mentioned?

[The Velveteen Ocelot]

7. Birds don't get ingested into jet engines very often.

Most of the time they hit some other part of the airplane. Sometimes small birds get sucked in (and it really stinks in the airplane when that happens) without causing the engine to quit, though it will have to be inspected for damage. A screen would involve considerable complexity - there's no compelling reason to add one.

[NutmegYankee]

9. It doesn't require rethinking - it's been evaluated and rejected.

Engineering is often like that -you evaluate the trade offs. The issues with a screen would likely require new engines and possibly redesigned aircraft as the engines would be heavier and produce less power. Those engines would also consume more fuel.

All to reduce a very low risk. Most double engine flame outs are due to ice detaching from the wing on rear engine jets or from intense hail before the CFM56 turbofan was redesigned.

[brush]

18. Thanks. Just thought there could be a solution.

[NutmegYankee]

21. For interest, the co-pilot of 1549 answers this question in this video

Starts at 49:30

[longship]

11. Mr. Spock, raise shields!

There are no shields from birds flying into jet engines.

[Travis_0004]

12. no shields, but we do have dogs and falcons working at airports, and thats just as cool.

[Warren DeMontague]

13. Jet engines as a technology are extremely safe and reliable.

I suspect as others have noted extensive risk/benefit analyses have been done on this question; and the conclusion is that given the infequency of bird strikes actually incapacitating an engine, the potential problems caused by a solution far outweigh any diect safety improvement on that issue.

[BlueCollar]

14. if the screen failed

Really bad things will happen.

[mnhtnbb]

15. "Sully"--with Tom Hanks playing pilot Captain Sullenberger--directed by Clint Eastwood

opens next Friday.

Certainly not a fan of Eastwood's politics, but he has directed some interesting films.

The film is based on Sullenberger's autobiography, Highest Duty, which he wrote with Jeffrey Zaslow.

[MicaelS]

19. I really want to see that movie.

From the first trailer it appears the NTSB went after Sully and his copilot in a ever harsh way. Trying to claim they could have made it back to an airport. I usually have very high regard for the NTSB, but in this case I think they're full of shit.

[NutmegYankee]

20. In the Air Crash investigation episode the NTSB said they made the right call

Only 50% of simulations made it back, but that was with an immediate effort to return - if they factored in decision time, all crashed. They had to investigate it though to come to that decision.

[XemaSab]

23. I'd guess that the river would give more room for error, a longer "runway" if you will

Since you couldn't go faster in the plane without losing altitude and you couldn't use thrust reversal to brake, seems like the risks of crashing before the runway or flying off the end of the runway would be substantial.

[NutmegYankee]

25. The NTSB found they wouldn't have even made the runway in nearly all cases.

What may upset people is the NTSB has to investigate all angles, and it angers people to question a hero's actions. But with a plane destroyed they had that responsibility. Some factors did result in recommendations to the FAA to madate changes to the Airbus Engine Dual Failure checklist. Items like the ditch switch and turning off ground proximity alarms.

[The Velveteen Ocelot]

26. I don't think they had time to complete the checklist,

and the ditching switch wouldn't have helped anyhow because the whole aft end of the fuselage cracked open when they hit the water. The NTSB is very thorough because they have to determine the causes of accidents - their job isn't to assign "fault" in the legal sense but causes in the technical sense. They are very good at this.

[NutmegYankee]

30. The report recommended a new format to the engine dual failure checklist.

If engine restart is unlikely, it now jumps straight to sections on forced landing or ditching. It was also redesigned for lower altitudes.

[LastLiberal in PalmSprings]

33. My understanding is the rear end didn't crack open

One of the passengers jumped past a flight attendant and started to open the rear door. The water started to flow in, lowering the rear of the aircraft into the river. Had he not done that, the aircraft might have floated level.

Correction: Several passengers testified it was a flight attendant who opened the door. http://tinyurl.com/zry5nq7 Either way, the result was the same.

[The Velveteen Ocelot]

34. Here's a photo of the impact damage.

The severe damage to the aft lower fuselage is described in detail in the NTSB report, at p. 31, here: http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR1003.pdf

The airplane was already taking on water because the fuselage was so badly damaged. The only thing opening the passenger door might have done would be to let water into the cabin sooner.

[LastLiberal in PalmSprings]

36. Thanks for the clarification.

I'd never seen that picture before.

[Travis_0004]

28. Planes have brakes

And those brakes are capable of stopping a fully loaded plane without the use of thrust reversal (often on an aborted takeoff where most of the runway was already used up getting to take off speed).

Assuming he could make the runway, stopping would not be a problem. Stopping using only brakes would have been extremely easy to do.

The danger is not getting to the runway, and that danger was very real.

[The Velveteen Ocelot]

31. Here's the catch, though.

With both engines inoperative the engine-driven hydraulic pumps don't operate. Without hydraulic pressure you can't operate the brakes or ground spoilers once the accumulators are exhausted, which doesn't take long. They would also have landed without flaps since those are also operated hydraulically, and this would have significantly increased their landing speed (and required runway length). The ram air turbine does supply some reduced hydraulic pressure to one of the 3 systems in an emergency but it's not enough to provide full braking power. You will also have only emergency electrical power from the RAT (which doesn't work below 140 kts) unless you can get the APU started, so you won't be able to power the electrical hydraulic pump either. Everything kind of goes to hell if both engines fail. You need a whole lot more runway if you land without engines.

[NutmegYankee]

37. One major piece of luck was one engine did idle for some time.

The core took damage and the fuel nozzles had been knocked free, so it wouldn't produce power (thrust) but it did keep the hydraulics going and give time for the APU to spin up.

I believe this may be a part of the plot of the upcoming film "Sully". While the engine was "running" it couldn't rev up for thrust.

[CrispyQ]

16. I saw a documentary last night called "Why Planes Crash."

It was fascinating. They covered the Hudson river landing, too.

[Travis_0004]

29. Taking off is optional. Landing is mandatory.

[trof]

22. I've had a few bird strikes.

Once just after lift off out of SFO one morning in a B-747.
Felt a thump and a slight vibration. Engine instruments all read normal.
You can't see the engines from the cockpit so I went down to the main deck to listen. It was a cargo plane, so no windows.
Couldn't hear anything unusual.
At about 10,000 feet the vibration stopped, so we proceeded to Anchorage.

At the gate we found some damage to the #2 (left inboard) engine.
Bless GE, they build a hell of a tough engine.

[The Velveteen Ocelot]

27. Once I nearly hit a bald eagle with a Cessna 172.

That would have been a little more problematic.

[Major Nikon]

32. Especially for the bird

[Stellar]

24. Yep, I've got it on my Roku.

[jmowreader]

35. If the screen broke loose from its mountings, IT would take out the engine