Q400 Safety Issues

As AirlineWorld reported earlier, all Bombardier Q400s were advised to be grounded for a security check following the accident of Scandinavian Airline’s flight to Aalborg on September 9, 2007.

Following the article, we received a comment from Mr Murray Cohen:

“I am a retired flight controls engineer. I have been following the Q400 accidents that occurred in Denmark and Lithuania very closely and consider these accidents to be very critical situations. These failures are giving the aircraft industry a subtle, but urgent warning that must be addressed. I found a report, dated September 15, 2007 online re – Preliminary Report on Danish SAS Q400 accident that included a very useful drawing for analyzing the failure mode. It would also be very useful to review a drawing or sketch of the main landing gear retract/extend actuator, manufactured by the Goodrich Corp. in Tullahoma, Tennessee in order to confirm my analysis of these failures. Please note that a nose gear incident occurred on a Q400 in Japan on March 13, 2007, and I suspect that it is probable that it contains a similar actuator design as the main landing gear system. Another nose landing gear accident occurred in Munich, Germany on September 21, 2007. If this is true, it would be very important to inspect the nose landing gear actuator as well as the main landing gear actuator. In my study of the main landing gear reports, some investigators noted the fact that the jam nut backed off and the lockwire was missing. This condition, could eventually cause a disconnection of the rod end, which was also stated by investigators in preliminary reports. This failure may have actually occurred after 10,000 cycles while coupled with severe impact upon landings. This scenario seems very plausible. Most of the hydraulic actuators used in the aircraft industry contain a locking device to prevent rotation of the actuator piston, and are secured by a jam nut, and lockwired to prevent the jam nut and the locking device from backing off. Early discussions regarding this failure were stated that corrosion in the linkage probably played a major role in the accident. I don’t believe that corrosion played a significant role in these failures. My intention is not to interfere with the official investigation of these accidents, but to offer a feasible scenario to help solve the problem.”

I wrote a letter to Bombardier and I was given the following answer:

“Investigations into the Q400 right main landing gear incidents in Denmark
and Lithuania are
still continuing, as are the investigations into the nose landing gear
incidents in Japan and Munich.

We cannot comment or speculate on the root causes of these incidents until
such time as
the authorities have concluded their investigations and issued  their final
reports. We can however advise
that on the basis of published preliminary reports and comments by the
authorities as to the focus of their
investigations,  there is no relationship between the two nose landing gear
incidents and no relationship
between those and the Danish and Lithuanian incidents.

We suggest you contact the relevant aviation authorities for more

I think it is a correct answer and naturally we will carry on and contact the relevant authorities. In the meantime Mr Murray has left for holiday, but we are waiting for his comment.

If you are interested in the follow-up of this conversation, please make sure to add our blog’s RSS to your RSS reader!

By Szafi 

6 Responses to “Q400 Safety Issues”

  1. 1 balint01 October 5, 2007 at 10:12 am

    Bombardier said that an estimated 149 of the global fleet of 165 Q400s have returned to full service following SAS’s and Wideroe’s combined reintroduction of up to 11 aircraft yesterday.
    (ATW News)

  2. 2 Lite October 8, 2007 at 1:45 am

    I just wrote today in my blog regarding how I don’t like flying – mostly because you need to trust so many different people (aircraft companies, pilots, etc.).

    A bit scary, don’t you think?

  3. 3 Murray Cohen, P.E.(RETIRED, FLIGHT CONTROLS ENGINEER) October 8, 2007 at 6:02 pm

    Thank you for responding to my comments.
    This is the proper response to my comments at this stage of the investigation. However, I sincerely hope that the relevant agencies take my comments seriously. If the nose gear hardware is different than the main gear, then my comment regarding the use of a locking device may or may not apply. However, it is very possible that the main landing gear actuator may require a locking device to prevent rotation in an environment of severe vibration during the flight regime and high impact loading caused during the landing mode. The use of a jam nut and lockwire without a locking device is not an appropriate device since it relies on friction for the security of the jam nut and tightening of the jam nut with the proper torque. The use of lockwire is not a positive device for preventing rotation of the jam nut., since using human factors in design considerations, the lockwire can be broken or inadvertently omitted. The typical method currently being used in the aircraft industry is the incorporation of a locking device in addition to a jam nut and lockwire. Typical examples of locking devices for male rod end applications are as follows: NAS513, NAS14227, NAS14198, NAS1193.

  4. 4 line October 29, 2007 at 1:21 am

    Hi – I am a student at the Danish Technical University, writing a project about the Dash 8 Q400s.
    I have seen some of the grounded SAS Q400 – and I know for a fact that there were found different grades of corrosion at the linkage on 26 out of 27 machines…. However, recently checked and regarded fit for fight, the landing gear collapsed again yesterday, causing SAS to ground all Dash 8 machines, for ever!
    This time, the collapse is expected to have a different cause than corrosion in the actuator – You might have a point regarding rotation – but could the jam nut back off so fast? so early after a full service?

  5. 5 szafi October 29, 2007 at 1:35 pm

    Dear line,

    thank you for the useful comment! We are very interested in what could have happened this time.

  1. 1 Flight 202 « Yonadav (yoni) Norman Leitersdorf - Is The Long Name a Compensation For Anything? Trackback on October 8, 2007 at 1:45 am

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