MDTyKe

Was anyone on UA 1721 yesterday SFO-KOA? I noticed it was delayed for quite a few hours, and during landing it had a hydraulic issue per local scanner. #3857 757-300; looks like it's set to do the red-eye KOA-SFO tonight 11/26. Did it have Mx prior to departure, and then something else prior to landing? As I understand it, a "Level 2" emergency is quite serious.

From a local radio scanner:

Maglev

I've been waiting to hear more about this--I read something on Facebook last night, from a Hawaii news source, that said there was a "total hydraulic failure."

MDTyKe

How would we know if there was Mx prior to departure? I'm just curious why it was so late to begin with. Looks like the hydraulics failed as it was coming into land. My guess is those 190+ people on board were very, very thankful. The lava rock around KOA has very little give..

Maglev

At least KOA has a long runway!

LarryJ

CONUS <-> Hawaii are ETOPS flights which always require an ETOPS inspection prior to departure so, at the very least, we know that was performed prior to the flight.

The hydraulic systems have multiple layers of backups.

The 757 has three separate hydraulic systems, each with two separate pumps and its own independent fluid supply . Each flight control is powered by at least two of the three systems for redundancy so all primary flight controls will continue to operate with one system out and complimentary primary controls, i.e. left aileron and right aileron, each have one system that the other does not so at least one of the two controls operate if two hydraulic systems are out. Other systems are powered by one, or more, of the three hydraulic systems. The pilots have procedures for handling any combination of hydraulic system failures and the airplane can continue to fly safely with any one system remaining.

It sounds like this flight lost one of the three hydraulic systems and landed with the remaining two systems operating normally.

The 767 also has three separate hydraulic systems but the pumps and the distribution of loads between the three systems is different. This is one of the bigger differences between the 757 and 767, at least from a pilot's perspective. Here's a pilot study guide for the hydraulic panels of the two airplanes that shows how each system is backed up and highlights some of the differences between the two airplanes.





RAT - Ram Air Turbine which provides hydraulic pressure to the flight controls if both engines have failed (used on AC143 in 1983)

PTU - Power Transfer Unit allows one good hydraulic system to pressurize another system which has lost its pumps without mixing the fluids. Basically a hydraulically-driven hydraulic pump. (It's been most of a decade since I flew the 757/767 and I don't remember exactly how the PTU is used) This is what makes the "barking dog" sound in the A320-series aircraft.

porciuscato

Amazing how much redundancy there is. I think RATs have been deployed fewer than 10 times in aviation history -- the famous Air Canada "glider" flight being one of them

buckeyefanflyer

Looks like they are using ship 3857 for flight 435 back to SFO running 5 hours late.

IAH-OIL-TRASH

I was on a flight from BOS-EWR which ended up returning to Boston. Back-up hydraulics (738) worked fine but fire trucks were scrambled anyway as a precaution. Not sure the KOA flight was in "quite serious" condition - probably scrambled responders as normal precaution.