Jazz Q400 Right main landing gear collapse YEG

[plhought]

...Seems to have been an issue with the Dash 8 dating back pretty much to day one:...

One should note that a significant number of those early serial number Dash-8's had much-much smaller ice-shields installed. Although their primary purpose is to prevent damage from flying ice to the fuse, they do help better protect the cabin from flying spinny bits.


I think we're getting a little side-tracked here - the propeller will always be a hazard. It's still disheartening that something like a blown tire could result in a collapsed gear. Even a violently shaking gear leg should have no problem keeping that H-Frame secure with over-centering, and spring-force.

[Canoehead]

should have no problem keeping that H-Frame secure with over-centering, and spring-force.

Over-center lock and hydraulic pressure.

[plhought]

Over-center lock and hydraulic pressure.

Sorry...and hydraulic pressure! :p

Seems like a heck of cheese holes lined up here mechanically to allow this thing to fail.

[Maynard]

Post irrelevant, thanks Canoe.

[Canoehead]

The Dash 8 100/200/300 also has composite blades.

[Oxi]

[CD]

Final report published:

Aviation Investigation Report A14W0177

Right main landing gear collapse
Jazz Aviation LP (dba Air Canada Express)
DHC-8-402, C-GGBF
Edmonton International Airport
Edmonton, Alberta
06 November 2014

Summary

The Jazz Aviation LP (doing business as Air Canada Express) Bombardier DHC-8-402, registration C-GGBF, serial number 4433, operating as flight JZA8481, departed from Calgary International Airport (CYYC) with an intended destination of Grande Prairie, Alberta. During the takeoff roll, the number 3 tire of the main landing gear failed. The flight was diverted to Edmonton International Airport (CYEG); aircraft rescue and firefighting equipment was standing by for the landing on Runway 02. On touchdown at 2030 Mountain Standard Time, the right main landing gear collapsed. Upon contact with the ground, all of the right-side propeller blades were sheared, and 1 blade penetrated the cabin wall. The aircraft came to a stop off the right (east) edge of the runway surface. Passengers and crew evacuated using all 4 exits. Three passengers sustained minor injuries. There was no post-accident fire. The accident occurred during the hours of darkness.

Findings as to causes and contributing factors

The number 3 tire ruptured on takeoff, most likely as a result of impact with a hard object.
During landing, the failed number 3 tire was spun by contact with the ground and was maintained at a rotational speed that was the same as or very close to one of the natural frequencies of the main landing gear. This caused the lock links to trigger the proximity sensor electronic unit to de-energize the solenoid sequence valve, thereby relieving system pressure from the extend port of the unlock actuator.
The excessive vibration caused the lock links to overcome the force from the downlock springs and unlock the stabilizer brace as a result of gear dynamics, which led to collapse of the right main landing gear.

Findings as to risk

If there are no specific requirements for dynamic vibration testing of components or completed airframes, there is a risk that similar or other aircraft systems could fail during high-vibration conditions.

Other findings

Short-radius turns with hard braking may cause an extreme shearing force on the tread area and on the sidewalls of the number 3 tire in particular, because it is the pivot point.

[YYCAME]

Well I for one am a bit disappointed in the results. To blame resonant frequencies feels like a bit of a shot in the dark. Unless they actually induced the frequencies on a landing gear and were able to observe a link lock/prox sensor failure in which case I would expect some sort of vibration dampening mod to be coming out as an AD. To claim that these vibrations were then induced by an unbalanced wheel spin also feels rather vague. This requires that the brakes were not being used or defective on that wheel, that the damaged hub was maintaining a very specific harmonic rather then decelerating with the aircraft or failing to decelerate due to normal friction in free rotation if no longer contacting the ground.

Did Transport really write this or were they just fed it by Bombardier? Anyone who has flown in a Q400 with the NVS deactivated would know that there are tons of vibrations going from the props, engines, wheel imbalance etc but somehow a wheel briefly spinning up on contract and then slowing down did all this?

[Canoehead]

Did Transport really write this or were they just fed it by Bombardier?

TSB wrote it. Nothing to do with Transport.

[YYCAME]

Your right TSB, though I think I assumed they were connected somehow. I'm not really clear on where the two overlap if at all.

It just seems much more plausible that a PSEU uncommanded signal to depressurize that actuator occurred because of an electrical design flaw where a signal failure defaulted to the wrong position. Though it is a bit disconcerting that the mechanical lock itself was not able to do its job, because hydraulic pressure loss is a normal part of life. Edit: Though maybe the actuator has been depressurizing for various reasons for a long time and the mechanical lock has been faithfully doing its job of covering up the problem.

[YYCAME]

Well maybe I jumped the gun after reading the blurb since the report itself shows they did some pretty thorough testing to reach those conclusions. It still seems like a design flaw that needs correction though before people get hurt next time.

[airway]

So.....

Other than not using retreads, and avoiding tight turns, there doesn't appear to be any fix to this problem other than redesigning parts of the landing gear system.


I guess for now, if you are a Q400 pilot, plan for a possible gear collapse if you blow a tire or have any other major vibration problem.

[old_man]

Hind sight being 20/20 it was a good call to ask for ARFF standing by for just a simple blown tire landing.

I always ask for fire trucks whenever I have something going on. I have had fire trucks chase me down the run way more times than I can remember. Every single time, it turns out, they weren't needed, I feel no shame. One never knows......

[linecrew]

...and avoid sitting in rows 5 through 7 if at all possible as a passenger.

[Heliian]

just a simple blown tire landing.

Well, that's an oxymoron.

A blown tire landing is never simple and should be treated as an emergency. There are way too many variables to take into account what will happen upon touchdown and roll out. Just keeping the thing in the middle will be next to impossible. Heck, some pilots have a hard enough time with a fully serviceable aircraft.


As an aside, if I was sitting in the punctured row seat, I would like to keep that chunk of blade and hang it up as a reminder of the challenges of flight.

[PostmasterGeneral]

We pay far too much in NavCanada and airport fees to not call the trucks out no matter what the incident may be. Besides, they love any excuse to get their big shiny trucks out of the station.

[old_man]

just a simple blown tire landing.

Well, that's an oxymoron.

My bad, I had put it in italics to denote sarcasm. As in; it is in fact not simple at all. I should have been clearer.

[Heliian]

Sorry old man, I kind of thought it may have been sarcasm but the written form is hard to decipher. The internet still hasn't figured that one out.

[Aux1]

This question was posed on another forum:

"The really big question is not about the tires or the brakes, but rather, what is Bombardier going to do the Q400 landing gear to ensure that in the future a vibration event does not result in a gear collapse..."

Tires, brakes, AFF, all interesting points of discussion but they don't go to the root of the problem.