AT THE HANGAR WITH BIG RICK

Why are my Thrust Reverser Doors Such a Drag?
(Challenger 300/350)

Welcome back! I hope you found the previous article about the Engine Inlet corrosion interesting and informative. Today, I would like to cover the other end of the Challenger 300/350 Engine: The Thrust Reversers (TRs) and the corrosion issues with the TR Doors. Why the catchy title? When deployed, the Thrust Reverser Doors do indeed cause Drag, in a sense, to slow down the aircraft upon landing.

Anyway, on to the real reason for this article: the corrosion issues of the Thrust Reversers. Owners, operators and aircraft maintainers understand that this is an area of real concern.

Let’s go through the process of detecting and correcting the problem.

The Bombardier Challenger 300/350 Thrust Reverser Door

Upon inspection of the TRs, the corrosion is easily detected by the decolorization and blistering of the protective coating. The coating and paint are removed to expose all the present corrosion. The corrosion is then removed, and the TR Door is gridded to prepare for NDT Ultrasonic Inspection.

The Ultrasonic Inspection is performed and recorded; each square is measured 5 times. The results of the Ultrasonic measurements are then compared to a Minimum Remaining Thickness Table for each zone.

If the TR Door passes NDT Inspection, that is great news! It is then painted, and a protective coating is applied. Lastly, it is installed back on the aircraft for maybe 2 or 3 years, until the corrosion rears its ugly head and the repair process must be repeated.

Wondering how many more times the corrosion can be ground-off before the remaining thickness is below the minimums? There is where the real concerns lie.

If the results are below the minimums, it is recommended by Bombardier to replace the TR Door. Excuse me? Have you asked for a quote on a new TR Door lately? Last time I checked, they were well over $200,000 bones, and there were none available.

In a nutshell, there are two problems.

  1. The protective coating is not doing a very good job of protecting the TR Door. The coating does have a tough job: constantly being bombarded with exhaust gases, moisture, temperature changes, etc.
  2. Once the doors fail the Minimum Remaining Thickness Test, the OEM recommends replacing the TR Door.

In a different, better nutshell, there are two solutions.

  1. Use a protective coating that will do a better job of protecting the TR Door from its harsh operating environment, or
  2. An authorized repair of the TR Doors that failed NDT, which will increase the thickness and protect the TR Door from further corrosion.

There are a few exciting new repair solutions out there. I have been involved in testing a few different types of coatings. I’ve only been involved in shop testing so far, but I’m looking forward to some real-world testing soon.

I’m also familiar with a few types of the repairs being performed on the rejected OEM TR Doors. Some look like they would work better than others and this would result in significant savings over buying a new TR Door.

In conclusion, all you Challenger 300/350 owners and operators…

THERE IS HOPE that the corrosion issues can be reduced or even eliminated. We’ll keep you posted. If you suspect you have corrosion issues with your Challenger 300/350 thrust reverser doors, then you should have an inspection as soon as possible for a repair or an overhaul. Contact CARE@CARE.aero to schedule an inspection.

BigRick

Rick Mutschler

Rick is a retired U.S. Navy chief with over 40 years of aviation experience. His passion for aviation took flight while serving on aircraft carriers in the Navy. Motorcycles are Big Rick’s other passion. While he’s always searching for the elusive 1958 Harley-Davidson Panhead, he’s the proud owner of a H-D CVO Road Glide and a Big Dog K9 Chopper. Every year, Rick and his veteran brothers burn rubber as they travel coast to coast in a long distance bike tour. CARE is proud to call Rick part of the family for 19 years and counting!