The Crash of Air Moorea Flight 1121: Analysis | Hacker News Reader

The Crash of Air Moorea Flight 1121: Analysis

medium.com

59 pointstroydavis13 comments

I'm a big fan of Cloudberg. His writing style is consistent, clinical, thorough, objective, and contextual. I highly recommend his analysis/timeline of the 2018 Camp Fire.

These are actually very durable great planes, often found on island routes with short runways like St Barth’s

Well written analysis of the failure

I live close to an airport that has a lot of commuter/short-haul routes. The Dash 8 is popular. Once you look at the Twin Otter and the Dash 8 side-by-side, you can't ever unsee the similarities! Now I just see these giant Twin Otters coming through every day!

https://en.wikipedia.org/wiki/De_Havilland_Canada_DHC-6_Twin...

https://en.wikipedia.org/wiki/De_Havilland_Canada_Dash_8

The comments pointlessly feteshize this accident investigation, but Air Moorea (and Chalk's Airlines) were both really the result of carrying passengers in worn-out airplanes.

Besides control cables, corrosion, fatigue, worn seat tracks and unavailable parts are also issues in these dinosaurs.

https://en.wikipedia.org/wiki/Chalk%27s_International_Airlin...

> In France, small aircraft like the Twin Otter were not required to have cockpit voice recorders, but Air Moorea had installed one anyway. This proved invaluable to investigators, so for the sake of future investigations, they recommended that all planes with capacity for 9 or more passengers be equipped with a CVR.

But earlier the author stated that the pilot

> uttered an expletive, the only word recorded on the cockpit voice recorder

So it doesn't quite follow how this crash caused the new regulations

The aircraft was not required to have cvr but it had one, which was invaluable to investigators, and do they decided other small aircraft should also carry one.

Stringing together the two quotes, it would appear that the expletive, the only word recorded on the cockpit voice recorder, proved invaluable to investigators.

Perhaps it is that simple, but it doesn't make sense to me how that expletive could have been so vital.

I can only think that it helped investigators formulate the timeline of exactly when things broke. However, that doesn't seem vital to the investigation, or something that couldn't have been determined with basic flight data recording.

The CVR also records other sounds that are audible in the cockpit - alarms, warnings and notifications, but also the sound of eg. a control cable snapping. I'd guess that was what they heard that was especially useful in this case.

"Air Moorea didn’t know it had both types in its fleet, it replaced all its control cables on the interval specified for carbon steel cables — about once a year."

Did they just ordered the replacement parts per catalog without looking at what exactly is being installed? I mean, they would have noticed that one plane has a different part number.

In this case, the author goes on to say the manufacturer had the same recommendation for both cables. Airlines that knew of the issue didn’t communicate with the manufacturer, and Air Moorea hadn’t identified the problem with the relatively new aircraft added to their fleet. The damage in the cable wasn’t visible in their regular inspections.

If I'm reading the report correctly, it's not clear they ever replaced the cables. The plane was new to the fleet (and was the only plane with stainless steel cables), and "Air Moorea specified on the parts follow-up documentation that the life of the rudder and elevator cables was limited to one year (operations in saline atmosphere) from 2 October 2006" (the cables had been checked and re-installed prior to handover). The accident occured 9 August 2007.

Furthermore, even if they had known, it's not clear it would have made a difference:

> Twin Otter cables can be made of carbon steel or stainless steel. These two types of cables are interchangeable on the airplane. Their inspection and replacement programmes are the same although their behaviour is different: carbon steel cables are more sensitive to corrosion, stainless steel to wear.

> The checks required by the manufacturer are based on the number of flying hours performed or on the calendar and not on a number of cycles. This inspection rhythm is well adapted for the phenomenon of corrosion but not for that of wear.

Absent their own experience with the cables ("Several operators had adopted special inspection intervals closer together than those mandated by the manufacturer"), would they have changed anything?

https://www.bea.aero/docspa/2007/f-qi070809.en/pdf/f-qi07080...

For more by Admiral Cloudberg, he has a subreddit: https://old.reddit.com/r/AdmiralCloudberg/

Reply on news.ycombinator.com