WestJet Pilots, seen this incident? Dual Hydraulic Failure

[invertedattitude]

Alaska Airlines 737-790

October 19, 2006

According to Alaska Airlines flight safety personnel, after entering Mexican airspace at cruise altitude, the flight crew was alerted to a System B hydraulic failure. The flight crew opted to return to the United States. Upon reaching United States airspace the flight crew declared an emergency and returned to LAX. While on a 5-mile final approach to LAX at 2,500 feet above ground level (agl), the flight crew selected flaps to 15 and extended the landing gear. About 800 feet agl, the flight crew was alerted to a System A hydraulic failure, and subsequently lost hydraulic quantity and pressure of System A. At that point, the airplane became difficult to control in the mechanical reversion mode; however, the flight crew was able to land the airplane without further incident at 0330.

Alaska Airlines maintenance personnel, a Federal Aviation Administration (FAA) airworthiness inspector, and personnel from Boeing examined the airplane and noted that the hydraulic failure of System B (the first event) was attributed to a catastrophic failure of the engine driven hydraulic pump. ASA maintenance personnel found a spoiler hydraulic line that had fractured and bled out the System A (the second event) hydraulic quantity leading to the dual hydraulic failure event.

Wondering if these types of incidents make it into newsletters or anything for you NG drivers?

Secondly as I've read in other places the odds of having a dual failure are through the roof. Also what is exactly Manual Reversion?

[Rotten Apple #1]

Hey Av8r...thanks for the article...where did you find it?

Manual reversion means basically flying without the assistance of the hydraulic actuators. As you can imagine, in a modern jet aircraft, the control forces at the flight control surfaces are quite immense...hydraulic assistance, along with "artificial feel" units enable the pilot to move the control surfaces with similar sensations to your basic cable operated airplanes.

The FBW Airbus products have a similar setup.

And yes, we NG drivers routinely receive safety reports and updates...from various sources. Just haven't read of this one...if you can supply the source, I'll cut and paste it to our Pilot Website's "Safety Section".

Cheers

John

[CD]

NTSB Identification: LAX07IA014

[Rotten Apple #1]

Thanks to both you guys. Linked to it, on our pilot's website.

[invertedattitude]

CD beat me to it, no problem on posting it John. Hopefully they will learn it was a strange coincidence and not an inherent system problem.

Safe flying.

[195psi]

The newer buses do not have mechnical reversion. They do have a RAT or ADG which will supply a small amount of hydrau.ic pressure. But then again they aslo have 3 hydraulic ystems, Blue,green and yellow. Loss of all hydraulics in a 320/330 or 340 is much more serious than on the 737NG's.

[Rotten Apple #1]

195...my previous bus time was 320/330 so excuse my ignorance pls

And comparing the two types, yup, much bigger affair on the bus, but definitely controllable with a smooth hand and patience.

[WJ700]

I'm usually happier with manual reversion, unlike one system out that gives a Yaw Damper failure. I have enough near death experiences in taildraggers thanks.

Good link, thanks fella's.

[mulligan]

Got in the sim one day, took off and turned off all 3 hyd systems. (I was thinking about the Bagdahd missle strike). A/c is quite controlable in roll using differential thrust however very squirrelly in pitch! I was able to land successfully on one of two tries.
The a/c oscilates in pitch. Add thrust and it will oscilate it's way to a higher altitude. Decrease thrust and it does the opposite. As far as I could tell you are stuck with whatever speed you had when the hydraulics quit, whether that is 200 or 300 kts. The latter would make for an interesting landing!!!

[invertedattitude]

Got in the sim one day, took off and turned off all 3 hyd systems. (I was thinking about the Bagdahd missle strike). A/c is quite controlable in roll using differential thrust however very squirrelly in pitch! I was able to land successfully on one of two tries.
The a/c oscilates in pitch. Add thrust and it will oscilate it's way to a higher altitude. Decrease thrust and it does the opposite. As far as I could tell you are stuck with whatever speed you had when the hydraulics quit, whether that is 200 or 300 kts. The latter would make for an interesting landing!!!

So with no Hydraulics you have no pitch authority other than thrust? Or I'm missreading something, no pitch trim available either?

[mulligan]

No hydraulics equals no way to move elevators or stab. Power is it for pitch!
When I flew the 737-200 there were two main hydraulic systems plus a standby system. Is the NG the same? I guess Airbus philosophy is that 3 complete systems negates the need for manual reversion capability. Not sure that I agree!

[Rotten Apple #1]

edited

[McDoo the Irish Navigator]

Hi John et al.

My sketchy memeory of the A-330 has a mechanical link between the trim wheel and the trimable horizontal stabilizer., but I won't swear to anything anymore.

Speaking of the -200/NG hydraulics, the only real similarity is that there is 3 systems, A, B, and Stby on each machine.
The -200 had a line that connected the A& B systems, rendering them not entirely separate. Problem has been addressed on the NGs. The two separate systems run all different systems that the -200 hydraulics. Hence the 180 min. ETOPS certification.

I'll add my comments on manual reversion. Took a -200 out of a C-check for a test flight and subsequent ferry to YYC. One on the items on the checklist to be completed was a manual reversion. I found it so much easier to fly than the simulator in the same mode. Truthfully, Ive found the 737s to be one pleasant surprise after another. I'd like to do the same thing again sometime on the Ng, but from that experience, I'm confident I could fly a very nice approach indeed, if necessary.

Your comment about the 150 brought back memeories of flying the Navajo from YSL to YFC just using power, trim and (gasp!) rudder. It's a good job I didn't spin the thing.

Keep in touch.

[mulligan]

The 320 also has a mechanical link to the stab...but you need hydraulic power to use it! Its a bit misleading to call it a mechanical link as we tend to consider that means a backup for loss of hydraulics. Not so.
I remember the 737-200 sim as being a bit hellacious in manual reversion...interesting to think that the airplane is better. Not surprising tough I suppose.

[grammar boy]

I did a test flight in the NG after some maintenace that required us to do a manual reversion. Flew quite nicely.

[Four1oh]

I did a test flight in the NG after some maintenace that required us to do a manual reversion. Flew quite nicely.

I've also flown the -200 in manual revision after a heavy check, and had no problem whatsoever. No issues landing in the sim either, but DAMN, it was fast!

[Troubleshot]

Here is a link to point out the differences as well as schematics. http://www.smartcockpit.com/b737/B737%2 ... NTROLS.PDF

as said before the 737-200 hydraulic systems ( A & B ) were connected as apposed to 737-300, -400-, -500 an NG's A & B systems that criss crossed the jet to different componets, the systems are not really connected except at the PTU (power transfer unit)

[roscoe]

Not to beat the topic to death, but the 737-200 hydraulic systems are able to interconnect on the ground, only, interconnect valve operates with a/c on ground and park brake set, and interconnect selected to open.