JetBlue plane's mechanical meltdown sends it 'careering wildly through the skies'

[Evan]

Originally Posted by snydersnapshots

I'm not an Airbus guy, but in Boeings the electric hydraulic pumps are in the wheel wells. I'm wondering if the grinding noise they heard was an electric pump eating itself--perhaps because of the problem (lack of fluid) or perhaps the cause of the problem.

The green system, the one that failed, does not have an electric pump. Its redundancy comes from the PTU link to the yellow system, which is also engine driven but has an electrical back-up pump (the blue system also has an electric pump, but no engine driven one).

I wonder is the sound was from the gear retraction mechanism eating itself due to lack of fluid (or something like that).

[guamainiac]

How about the SAS A330 that was forced to cut it's Copenhagen trip short by a forced landing in Bangor Maine after the cockpit filled with smoke yesterday?

Any clues on the cause?

[snydersnapshots]

Originally Posted by Evan

I wonder is the sound was from the gear retraction mechanism eating itself due to lack of fluid (or something like that).

I'm not sure of the location (those on here more familiar with the Airbus may have better insight) but I suspect the sound was the PTU running. Essentially, it's a hydraulic motor driving a hydraulic pump. I know the PTU's on the Boeings make a fair amount of noise.

[Evan]

Originally Posted by snydersnapshots

I'm not sure of the location (those on here more familiar with the Airbus may have better insight) but I suspect the sound was the PTU running. Essentially, it's a hydraulic motor driving a hydraulic pump. I know the PTU's on the Boeings make a fair amount of noise.

That would make perfect sense. Do you know if/why this might cause a yellow system overtemp?

From wiki:

The PTU on the Airbus A320 family of aircraft makes a distinctive noise resembling a barking dog or sawing, and is quite audible from inside the cabin. Passengers on board A320-family aircraft are therefore very familiar with the sound of the PTU, but few know what it is.

Oh I know this sound. I hear it sometimes during taxiing, when one engine is shut down. Arf Arf Arf. Not a "screeching" though.

[snydersnapshots]

Originally Posted by Gabriel

Again, they had ONE hydro failure, another hydro overtemp (don't know exactly what part), and a third hydro Ok. The overtemp was worked around so they continued with two hydro systems.

Not saying that it was necesarily wise (or the contrary), but it's not like they circled around for 3 hours with only one hydro system left.

My initial response was to question the wisdom of flying with one dead and one overheated hydraulic system, then I found this:

http://www.aaib.gov.uk/cms_resources...EZDM_08-09.pdf

It appears that a green failure followed by a yellow overheat is not unheard of.

Originally Posted by Gabriel

The same applies with a fuel dump system. The FAR requirement for an MTOW landing doesn't even mention an eventual fuel dump system.

Gabriel, you caught me--running away at the keyboard without all the information. I looked through Part 25 and discovered you are correct. Upon further analysis, I came across this copy of Boeing's AERO magazine that talks about overweight landings.

Page three talks about the requirements:

"Overweight landings are safe because of the conservatism required in the design of transport category airplanes by FAR Part 25.

FAR criteria require that landing gear design be based on:

• A sink rate of 10 feet per second at the maximum design landing weight; and
• A sink rate of 6 feet per second at the maximum design takeoff weight.

Typical sink rates at touchdown are on the order of 2 to 3 feet per second, and even a “hard” landing rarely exceeds 6 feet per second. Additionally, the landing loads are based on the worst possible landing attitudes resulting in high loading on individual gear." [bold and italics are mine--Ken]

I wasn't flying so obviously I don't have all the information the pilots did. That being said, my vote would be, to paraphrase Larry the Cable Guy: "Git er down."

Thanks for getting me into the books!

[Evan]

Originally Posted by snydersnapshots

My initial response was to question the wisdom of flying with one dead and one overheated hydraulic system, then I found this:

http://www.aaib.gov.uk/cms_resources...EZDM_08-09.pdf

It appears that a green failure followed by a yellow overheat is not unheard of.

It follows then that the case here was probably a loss of fluid as well. I wonder if it was due to the same 'close door' actuator hose failure? The reports mentions:

Leakage from these hoses had been experienced a number of times before, so the operator has imposed a 6,000 flight cycle life on the hoses until the aircraft manufacturer devises an engineering solution to the problem.

The operator... why not the FAA?! Why is this not an Airworthiness Directive?

[snydersnapshots]

Originally Posted by Evan

That would make perfect sense. Do you know if/why this might cause a yellow system overtemp?

From wiki:



Oh I know this sound. I hear it sometimes during taxiing, when one engine is shut down. Arf Arf Arf. Not a "screeching" though.

I'm thinking the additional strain put on the yellow system pump by the PTU causes it to heat up. This, coupled with the heat generated by the PTU itself, heats the fluid above the temperature that triggers the overheat indication. (Just did a quick look on the internet for an Airbus Manual and found that an "PUMP OVHT" message is caused by the electric pump overheating and a "RSVR OVHT" is caused by an overheat of the fluid returning to the reservoir).

On Boeing airplanes the heat-exchangers for cooling the hydraulic system are in the wing fuel tanks. Though I didn't see any indication in the manual I found, it wouldn't surprise me if the airplane had a similar system. Given that this happened in Las Vegas, I could see a scenario where the fuel in the truck was heated by the sun and then put in the airplane, which was also heated in the sun. Thus, the already warm fuel wasn't dissipating heat very well.

[Evan]

Originally Posted by snydersnapshots

I'm thinking the additional strain put on the yellow system pump by the PTU causes it to heat up. This, coupled with the heat generated by the PTU itself, heats the fluid above the temperature that triggers the overheat indication.

Actually the AAIB bulletin you posted explains it:

The PTU uses hydraulic power from one system to power the other in case of a loss of pressure. However, if the loss of pressure is caused by a lack of fluid, the PTU will overheat about two minutes after starting

Note: this was an Easyjet A319.

[snydersnapshots]

Originally Posted by Evan

The operator... why not the FAA?! Why is this not an Airworthiness Directive?

It very may well have been an AD (probably by the British government since the subject airplane is registered there) but the operator imposed a more restrictive policy for replacing the lines than the AD required. I searched for AD's of this nature but wasn't able to find one. Not that it's not there...

[Black Ram]

Originally Posted by Evan

Oh I know this sound. I hear it sometimes during taxiing, when one engine is shut down. Arf Arf Arf. Not a "screeching" though.

Here it is:

http://www.youtube.com/watch?v=RftOD_O7Taw

http://www.youtube.com/watch?v=9ffJgk1-tCA

[phoneman]

Originally Posted by UncleFire

Probably a dumb question but... How is it that they can't dump fuel?

I can understand with implications noted above that they wouldn't necessarily want to land w/out certain functions, but to stay up in the air 4 hours?

With hydro systems being flaky, I'd think they'd want to address what they could, dump fuel and land as soon as practical.

EDIT: Google, as usual is my friend. I see that a320's cannot dump fuel so I guess that renders my question rather moot.

Why was the plane designed not to be able to dump fuel?

[snydersnapshots]

Originally Posted by phoneman

Why was the plane designed not to be able to dump fuel?

The requirement to dump fuel is related to the climb performance of the aircraft if it should lose an engine. Here it is in a nutshell in this excerpt from the AERO magazine referenced in my earlier post:

"FAR 25.1001 — Requires a fuel jettison system unless it can be shown that the airplane meets the climb requirements of FAR 25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprising a takeoff, go-around, and landing at the airport of departure."

If you have a bad case of insomnia or are just so bored that you want to read it sometime, here is a link to FAR Part 25 (aka 14 CFR Part 25). You have the chapter numbers listed above for reference: 25.1001 gives the requirements for the fuel jettison system and 25.119 and 25.121 (and those around them) discuss required performance...climb gradients and such. I don't suggest reading them while in the john (WC/blue-room/bathroom/crapateria or whatever slang term you prefer) because I'd hate to see you hurt when you fell asleep and thus fell off the commode.

[Evan]

Originally Posted by snydersnapshots

"FAR 25.1001 — Requires a fuel jettison system unless it can be shown that the airplane meets the climb requirements of FAR 25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprising a takeoff, go-around, and landing at the airport of departure."

Is this to ensure that the plane can execute a missed approach at MTOW-15mins fuel?

[Gabriel]

Originally Posted by Evan

Is this to ensure that the plane can execute a missed approach at MTOW-15mins fuel?

Yes.

[Evan]

Originally Posted by Gabriel

Yes.

So it is structurally safe to land at MTOW-15mins fuel, but not procedurally safe. So if everything is stable you burn off fuel, but if, for instance, a fire breaks out, you take it in knowing you might have to get in down in one.

Question in my head is: for an A320 with four hours of FOB, does it really take three hours to burn off enough fuel to meet the conditions of the FARs?

[Gabriel]

Originally Posted by Evan

So it is structurally safe to land at MTOW-15mins fuel, but not procedurally safe.

In airplanes that ARE REQUIRED to have a fuel dump system, yes (some airplanes do have the system while they have the performance required to get away without one). Airplanes that are required to have a fuel dump system are also required that such system must be able to bring the plane's weight below the weight needed for the go-around required performance within 15 minutes.

In airplanes NOT REQUIRED to have a fuel dump system, it is both structurally safe to land at MTOW and "go around" safe to do it at MTOW -15 minutes.

So if everything is stable you burn off fuel, but if, for instance, a fire breaks out, you take it in knowing you might have to get in down in one.

In an airplane with fuel dump system, if you badly need to land, you dump system while you return to land. You land at whatever low weight you have managed to get.

In an airplane without a fuel system, you return and land period.

In bot cases, a point can be made that the pilot should check whether the weight is "MTOW-15" before going too low during the approach, or he might be unable to go-around if needed.

However, if the emergency is very severe (like a fire), I personally would risk having to go around with less than 100% of the the minimum required climb performance (that will still be a positive climb).

Question in my head is: for an A320 with four hours of FOB, does it really take three hours to burn off enough fuel to meet the conditions of the FARs?

Even taking-off at MTOW, any plane meets the FAR requirements for landing weight as soon as it initiates the take-off run and the FAR requirements for go-around performance at most 15 minutes after that (in planes that require fuel dump system, that includes dumping fuel during those 15 minutes).

[Evan]

Originally Posted by Gabriel

In airplanes that ARE REQUIRED to have a fuel dump system, yes (some airplanes do have the system while they have the performance required to get away without one). Airplanes that are required to have a fuel dump system are also required that such system must be able to bring the plane's weight below the weight needed for the go-around required performance within 15 minutes.

In airplanes NOT REQUIRED to have a fuel dump system, it is both structurally safe to land at MTOW and "go around" safe to do it at MTOW -15 minutes.



In an airplane with fuel dump system, if you badly need to land, you dump system while you return to land. You land at whatever low weight you have managed to get.

In an airplane without a fuel system, you return and land period.

In bot cases, a point can be made that the pilot should check whether the weight is "MTOW-15" before going too low during the approach, or he might be unable to go-around if needed.

However, if the emergency is very severe (like a fire), I personally would risk having to go around with less than 100% of the the minimum required climb performance (that will still be a positive climb).


Even taking-off at MTOW, any plane meets the FAR requirements for landing weight as soon as it initiates the take-off run and the FAR requirements for go-around performance at most 15 minutes after that (in planes that require fuel dump system, that includes dumping fuel during those 15 minutes).

So... why did they circle here for three hours? Not to meet landing weight requirements. To work the problem? I assume they could get through the checklists and prepare everything in under one. The green system was lost, but it is not needed. The yellow system seems to have simply been a transient overheat due to the PTU and I expect that it would have been restored by then. I'm sure there are other complications. It will be interesting to read the report of this one.

[Gabriel]

Ok, maybe I oversimplified.
There are TWO maximum landing weights required by the FAR.
The MLW and the MTOW.

The FAR requires for a landing MLW that the plane "survives" a harder landing that at MTOW (which is still more than your usual hard landing), so there is more "regulatory"(*) margin when landing at MLW than at MTOW.

Additionally, a landing above MLW:
- Can overheat the brakes
- Requires an overweight landing inspection (that could be as simple as plugging a laptop in a port and checking the landing Gs)
- There is more fuel to feed a fire in case of an accident
- Landing 8and crashing) speeds are higher
- Loads on the tyres/landing gear are higher
- More runway is needed

Because of all that, a balance is made between advantages/disadvantages of an overweight landing, depending on the type of emergency. When there is urgency to land, you land at whatever weight with the peace of mind of knowing that the plane is designed to do so (but maybe with a tad more of caution than usual to avoid a too hard landing).

Fire is an obvious case. Double hydro failure too. And so is engine failure in a twin.

At the other extreme of the spectrum, you have landings for which you would probably not only burn enough fuel to be below the MLW, but you'd probably want to land with minimum weight fuel. An example could be a gear-up landing.

In the middle, you have an assortment of problems for which the situation is not that severe that you feel the need (or the procedures call) to land ASAP but you also don't feel like crossing the Atlantic ocean (or getting far from the airport) in that condition. In those cases you burn or dump fuel to get to the MLW. A single hydro failure seems to fall in this group.

(*) Believe or not, sometimes a landing at MLW can put higher loads on parts of the structure than an MTOW landing, so you'd have more margin at MTOW than at MLW, although both would be more than the margin required by the MLW landing.

[JJR]

I probably missed it 5 or 6 times, but what was the tail # for JBU194 that day?

[UncleFire]

Originally Posted by Black Ram

Here it is:

http://www.youtube.com/watch?v=RftOD_O7Taw

http://www.youtube.com/watch?v=9ffJgk1-tCA

Flying out of Phoenix I hear the 2nd version pretty much every flight (on Air Bus A/C). Upon landing not as often IIRC.

I rarely hear it in flight and that 1st one didn't sound good at all.

I compare it to the sound of a hand-saw being used on wood.