I Want to Buy a Mooney TLS

What Should I Do?

By Joe Frisolone
East Coast Aviation


{Originally printed in the July 1999 issue of the MAPA LOG, the Mooney Aircraft Pilots Association monthly magazine}

In the first article regarding prepurchase inspections we discussed the Do's and Don'ts of a general nature. Now we will discuss the intricacies of the Mooney TLS/Bravo model number M20M. Mooney first manufactured the M20M TLS (Turbo charged Lycoming Saber) in 1989 and production continues today with the Mooney Bravo. What is the difference between a Mooney TLS and Mooney Bravo? The most significant difference is the cylinder heads. The Mooney TLS was manufactured with a Textron Lycoming TIO 540 AFIA, Turbocharged after cooled 270 horsepower engine. The Mooney Bravo is manufactured with a Textron Lycoming TIO 540 AF I B, turbocharged after cooled, oil cooled exhaust valve guides, 270 horsepower engine. The Bravo utilizes the "wet head" cylinders which promote improved exhaust valve guide wear. The TLS originally utilized "normal" parallel valve type Textron Lycoming cylinders which had a tendency to experience premature exhaust valve guide wear has substantially subsided if not entirely disappeared in the Mooney Bravo. In 1996, Textron Lycoming offered all TLS owners the option to convert their engines to the new style 11 wet heads" via Textron Lycoming Service Instruction # 1479A. Textron Lycoming was very interested in seeing all TLS drivers convert their engines. Pursuant to this they offered a financial incentive to perform the conversion, even for those owners who were well outside of the original warranty expiration date. When pursuing a used TLS/Bravo the first thing you should is ask is the type of cylinders installed. Based on the previous explanation, you want to make sure that the aircraft you are considering has the "wet head" conversion if it is a pre-1996 aircraft.

As I stated in the previous article, I like to fly the aircraft initially to test the operation of the avionics and other systems that just do not test properly on the ground. Also, I then have an engine that is as close to normal operating temperature as possible when performing a differential compression test. After the test flight, perform a differential compression test and record the readings. You can reference Textron Lycoming Service Bulletin #1191A or subsequent revision for pertinent information relating to differential compression checks performed on their engines.

What are acceptable or good compression readings? That will depend on a few different factors. The total time of the cylinders, the relationship of all cylinder compression readings compared to each other and what the compression readings were the last time a differential compression check was performed. Also, when comparing the differential compression readings subsequent to the current readings, the amount of flight time that has elapsed has relevance.

As a general rule regarding compression readings for a TLS/Bravo, 70/80 is considered good.

Where I have mentioned suspect a problem, I mean just that. There are usually significant reasons why compression readings are low or change rapidly, however, I have also experienced cylinders that "repair themselves" 50 hours later. My point is to consult with your maintenance professional before passing judgment.

Moving past the all important differential compression test, what else should I examine and check inside the engine compartment of a TLS/Bravo? Well, there are several things. I think it will help those that are reading this article with an "approach to minimums" concentration level if I list each in bullet fashion:

While I have mentioned numerous "things" that should be checked when performing a pre-purchase inspection of a Mooney TLS/Bravo, I did not mention all. My intentions were to concentrate on those items that are either repetitive, expensive to fix or safety related. When you hire Maintenance Technicians to perform a pre-purchase inspection they should also inspect the "little things". Such as the condition of the flexible cooling air baffles, the condition of the ignition harness, the flight control rigging, so on and so forth. As I mentioned in the previous article, MAPA Log June 1999, make sure you hire Maintenance Technicians that have TLS/Bravo experience. If you adhere to the tips I have given you, hire experienced TLS/Bravo maintenance professionals, your "new-to-you" TLS/Bravo ownership experience will be out of this world!

Go ahead, go for it. Treat yourself to Mooneys Brightest Star. Go on, get yourself up to 25 thousand feet, true out at 225 knots, catch a tall wind and then check out what the GPS says---it will astound you!