Wouldn’t happen on a 787.
Thanks, very interesting. I didn’t know that they could be lowered manually, but it makes sense for such a critical system.
737-800 doesn’t have a RAT (from my friend a 737-800 Captain).
There has to be significant elements of CRM going wrong to have contributed to this. Again this feels like it is hanging the pilots out to dry, but it has been discussed repeatedly many many times that in certain countries/cultures the CRM training/specifically the ability of the FO to speak up when the Captain may not be making the best decisions can be very limited. This has been evident in numerous other accidents in the past.
The YouTube video from the 777 pilot posted above has a demonstration (at 12:18) of the manual release of the landing gear. Does not appear to require a feat of strength.
In the above video he shows how it is done…basically just pull a ripcord, one for each set.
I just did the test on one of our 737s last month after we removed and reinstalled the main landing gear assemblies for a separate eddy current inspection in the area. It’s 18 pounds of force for the nose landing gear and 80 pounds for the main landing gear (I may have those backwards). The cables run from the floor of the flight deck to the uplocks at each gear and it uses gravity to allow the gears to “fall” on their own. A spring mechanism on the side braces helps them to lockout when they’re fully down. They cannot be raised without hydraulics, though.
It can be a chore for the First Officer to do it (they’d be the one sitting closest to it in the right seat), but I bet my ass could do it if I really wanted to get the gear down. 80 Pounds sounds like a lot, but the action is pretty smooth and kind of satisfying when it finally gives.
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Do you know if it’s possible that some hydraulics worked but others didn’t? One point made by the 777 pilot is that the plane is being oriented (directly over the runway) so the hydraulics needed to control the left/right steering of the plane were working.
Thanks for talking down to me and letting me know which pilots to avoid (such as yourself)
I’ll go to the FAA and let them know I should redo my instrument training and the Alaska Airlines pilot has some 25,000 hours that did my training, he led me on wrong.
Eyeroll
It’s possible, but a lot would have to be going wrong.
Each engine has its own AC generator and engine driven hydraulic pump. There’s also two separate, independent electric motor driven hydraulic pumps in the wheel wheel as a backup for when we do maintenance and need hydraulics. So, the No. 1 engine provides hydraulic power for the “A” system and No. 2 engine provides hydraulic power for the “B” system. Both “A” and “B” systems provide hydraulic power to a lot of the same aircraft components, but the “B” system does most of the heavy lifting. There’s also a Power Transfer Unit (PTU) in the wheel well in case one system fails. This PTU will help shoulder the additional load and allow the working hydraulic system to provide hydraulic power to the opposite, failing system.
Assuming that they took the No. 2 engine offline (“B” system hydraulics) after the compressor stall event (possible bird strike) and the No. 1 engine (“A” system hydraulics) was still working fine, the PTU would have opened a valve and allowed hydraulic pressure from the “A” system to help power the critical components that would have been powered by the “B” system (namely the flight control surfaces).
I don’t know what the policy is for the airlines, but the pre-landing checklist for every aircraft I’ve ever flown in has us turn on our Auxiliary Power Unit (APU) located in the tail section (not all aircraft have them). It’s a small turbine engine that drives its own AC generator and provides bleed air for engine starting. Most importantly, it would be used to provide critical AC power to the aircraft in case one or both engines went offline (AC power for instruments, electrical hydraulic pumps, etc.).
Apologies if I’ve muddied it up, I’m trying to prep for dinner!
At this point, is it normal for there to be no info being released about what they know. Im assuming that the crew was in contact with air control, somthere has to be some basic info about what the situation was. Seems strange that they have released some of that basic info of what was going on after a day and half. Maybe its normal to just be silent up until all facts are known?
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I worked at Boeing when the 757 and 767 were rolled out (way back in the early 80s). On the first flight of one of them in which they raised the landing gear (as I understand it, they leave the landing gear down on the maiden flight), one of the landing gear didn’t lock into place when lowered. So, gravity and the air load didn’t work…until the test pilot initiated a roll that banked the plane enough that gravity finally pulled the landing gear into locked position.
On another early flight, the spoilers didn’t deploy, and the plane was landed at way over the typical landing speed (like ~200mph?).
All from a faded memory, so apologies in advance if I mis-remembered something.
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I appreciate all of the helpful technical insights from which several people on this forum have contributed I expect it will come down to mechanical failures that intuitive and talented pilots could have overcome without great loss of life. My former neighbor and retired Southwest pilot who flew multiple fighters in the air force said that flying was easy under ideal conditions. (‘Easy ‘ being a relative term). However, when there is bad weather or a mechanical failure you want an experienced pilot at the controls — former military especially.
Yes, so the main landing gear has two braces, a side and a drag brace. These braces use springs and an over center mechanism (think the locks on ladder). The thing is that it is a statically indeterminant system ( Statically indeterminate - Wikipedia), so really nice one brace locks the system is stable and the other one may not lock. So to get both to lock you are dependent on deflections in the system.
What they do (on 787 and 777, don’t know about the 67 and 57, but assume it is similar), they have an eccentric bushing in the drag brace, so the length can be set. Basically so that it is “short” and may not lock when extended on the ground, but in flight air loads stretch that brace to the right length so they both lock.
I believe the incident you are referring to is the drag brace locked, but the side brace didn’t. So the pilot rocked the plane side to side to get more side load, that stretched the side brace enough for it to lock. If it was the drag brace, the pilot would accelerate to increase drag loads.
Also that didn’t happens during a normal extension, it happened during an alternate extension, but on the 757 and 767 the alternate extension uses hydraulics to drop the gear. A normal extension there are hydraulic actuators to lock the gear and you are not using the air loads to lock the gear.
Some key words in your sentence: “based on the limited known facts”; “it’s reasonable to discuss why they did what they did.”
We have no idea what the crew were facing. As of now, it is all just speculation. Anyone throwing up in-depth YouTube videos explaining what happened is doing so for viewer engagement.
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It is possible that will happen, but it is certain that the airfield itself contributed to the loss of life. If the building at the end of the runway was fragible things would have been different. When you have different standards than the rest you have to explain why.
Thanks for the technical insight. Can you confirm the PTU is for retraction only?
Further to the great insight from Chappy et al, the manual extension is practiced in the sim. The frequency of that depends on the particular training program, which is also evidenced based - meaning events that the operator has been exposed to will also guide the content of the training above and beyond the minimum requirements.
On every type I’ve flown, after manually extending the gear (releasing the uplocks and letting the gear free-fall), the checklist calls for yawing the aircraft using the rudder, to assist each manin landing gear to aerodynamically be down and locked. Essentially I would yaw the aircraft to the right - and the airflow would catch the inside of the right main landing gear forcing it outboards to lock in place. Rinse and repeat on the left.
Whilst a reasonably quick operation, the checklist will take some time to find and execute - electronic checklists help. What should also be borne in mind is that this was an unexpected event which appears to have triggered the crew to assess that an immediate return - conducting a teardrop onto the reciprocal runway rather than a circuit, or even better the standard missed approach, holding off to re-assess and configure the aircraft. The emergency extension isn’t just pulling the emergency gear extension handles and five seconds later your gear is down and locked.
I stated what happens on my aircraft to try to illustrate that there would be a lot going on and systems to reconfigure. From the videos and loss of transponder information, it is reasonable to assume that they lost power.
Starting the APU is possible airborne on most types, but usually comes with resultant drag. What appears to have happened is the crew prioritised low drag to ensure they made the airfield. The approach to land was controlled and aligned with the runway, which does suggest this was deliberate and the landing gear being retracted was not unexpected.
Asian cultures can have specific CRM issues. Western cultures are not above those either (Tenerife); but modern CRM focusses on empowering the monitoring pilot to call out any deviations. I fly with Asian pilots and would suggest the CRM issues are not so much geographically/racially cultural, but a result of the organisational cultural.
No, not for retraction. Off the top of my head, the PTU is meant to provide hydraulic power to some of the flight control surfaces, particularly the leading edge flaps and slats in the event of a loss of “B” system hydraulic power (a la the No. 2 engine).
I’ll have to dig out my training courseware to verify what I’ve written about it.
Thanks.
I understood the system which provides emergency slat/flap was the standby system, fed by the standby reservoir and see that the nomenclature is the PTU, whereas the LGTU relates to the landing gear.
The context of the discussion was exactly what hydraulic power they would have had available. The loss of ADS-B data suggests some form of electrical disruption, whether as a result of the initial birdstrike which has been speculated as the trigger for initiating the missed approach. This looks to have potentially affected ENG1, which would disable HYD A, which I understood would only leave the. manual gear extension as an option. If the crew secure ENG1, then there is video of ENG2 surging as a result of bird strike during the climb out after the missed approach (gear retracted, and slats/flaps were partially extended in that video, which would suggest they were cleaning up.) I can understand why, at this point, the crew elected for an immediate return with one engine shutdown - either deliberately secured or not - and ENG2 giving unreliable thrust. Add in the high workload, and the cockpit would have been exceptionally busy. A NITS briefing seems to have been given as evidenced by some passenger texts.
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