(Updated 28 DEC 2020) DHC-6 Twin Otter MLG Leg failures remain a concern 40 years after the first failure occurred in 1978 to Panamanian air force “Corporal Roberto xxxxxx” who was then a technician backing an aircraft into its parking spot (I don't recall his family name). His commander initially thought Roberto had caused the incident by mishandling the aircraft while parking the aircraft (used reverse to back into the parking space. Fortunately Roberto avoided the firing squad and survived to travel to Field Aviation West in Calgary ac "his" damaged Twin Otter accompanying Jack Gilbert, Mark Haid, Brian Schroeder, Rod Dixon and I took Roberto under our collective wing. Given Roberto had never seen snow, or played in snow it was decided to bring him with us for a weekend ski trip to Whitefish Montana USA on a Canadian private aircraft (Mark Haid was the pilot that day) for a weekend of skiing without Roberto having US visa (1978) to enter the USA! We did a lot of talking and made promises to the US border guard who eventually agreed to allow him in with our promise we would take him back to Canada! The border guard also pointed out that Roberto might be refused entry back into Canada as his Canadian visa was the single entry variety! We were young and didn't worry too much about borders in those days! We managed to talk Roberto back into Canada, a good trip except Roberto returned to Calgary with a lower body injury from his first experience with snow at Big Mountain Ski Resort. Apparently the Canadian Border Guard called our boss at Field and requested that we all be made aware how serious an incident we created making it clear Roberto was only permitted back to Canada as a result of him using his discretionary authourity. This story ties me directly to the first main landing gear failure and was a factor in my decision to challenge what had become “we all know its done” (which I concurred with), but no way to show compliance for -3 and -4 gear assemblies. The higher gear dash numbers were shown complinace via the IPC! So it was time to take a run at CF-80-06.
Transport Canada AD CF-80-06 was never a well written AD. Industry treated it as a nuisance and irrelevant. I 2014 when Viking submitted a request for AMOC, however the review was not complete . CF-80-06 was cancelled in January 2019 by the issuance of CF-2019-02.
I have assembled some related documents leading to CF-2019-02.
Most of us would have failed to comprehend the nuances of CF-80-06 to properly decode this AD because rather than the AD calling out the affected MLG legs by PN and SN, they chose to ignore that part of it. It was necessary to use the IPC to determine which gear dash (-) numbers were “pre 6/1660”. A “-3” gear is pre-6/1660 which means one must show compliance for SB 6/380. None could be produced by the seller of the Twin Otter even though the gear was “0” TSO from Field Aviation using the most current OH process. I provided an explanation along with a request to Field to provide a revised Form 1 to indicate that 6/380 / mod 1660 was performed. Denied! I will skip the details. My next step was to speak with the MDM managing the import/export, he forwarded my email onward to David Sword , a TCCA Airworthiness inspector who was the MDM’s PMI , who also happened to be assigned to Viking. A stroke of luck! Within a coupl eof hours I had received a draft (unsigned) AMOC…..dated 2014!
AMOC No. AARDG 2018/A63 is contained in the documents linked to this post.
Its clear from the AMOC "references" that Viking recognized a problem with this airworthiness directive in 2014, however the Viking request was cancelled by Viking before the AMOC which was approved and awaiting for execution by a senior TCCA manager. The AMOC is the result of an inquiry made by me to TCCA about a "C6UMxxxx-3" main gear leg installed on an aircraft that I was acting as buyers broker. The aircraft was being imported to Canada for immediate export to buyers country.
The incident in Indonesia last week may have been the result, in part, from challenges interpreting AD CF-80-06. Then in 2012 a "broken link" began when V6/0016 was issued. Companies that have not recently updated their approved maintenance programs should consider incorporating the the current AWL manual requirements include the current mandatory Overhaul requirements and applicable intervals for the main gear legs.
If in doubt about the airworthiness of any MLG leg, I suggest you contact Jack Gilbert (yes the same Jack in the story) <jgilbert@fieldav.com> at Field Aviation for a quote for the latest overhaul procedure. Field also manufactures new landing gear for classic series spares and the Series 400 so are the global "hands on" experts.
This issue appears to have become acute in 2012 but even before this date, the AD relied on a pre / post mod 6/1660 status for effectivity which is an airframe mod, not something marked on the gear data plate. Gear legs move from plane to plane so a airframe log entry for 6/1660 is not a valid determinant unless your aircraft has the original legs installed from aircraft manufacture / new.