I Want to Buy a Mooney TLS What Should I Do?	By Joe Frisolone East Coast Aviation

 

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.

• 70/80 would not be great numbers if the cylinders were only 100 hours since new but would be great readings if the cylinders have 1500 hours since new.
• If five of the cylinders varied from 70/80 to 74/80 and one was 58/80, I would investigate the cylinder that was 58/80. When one cylinder compression reading varies that much from the othrs, suspect a problem.
• If the compression readings varied from 70/80 to 74/80 at 500 hours since new and then another differential compression test was performed at 600 hours since new and one cylinder changed to 62/80 while the others were around 68/80 to 76/80, suspect a problem with the cylinder that is 62/80.
  

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:

• Make sure all of the cylinders are current with Textron Lycoming Service Bulletin 388B, procedure to determine exhaust valve guide and condition. In the field we call this, "Valve wobble test". Recently, Textron Lycoming revised the time interval for certain cylinders to every 1000 hours of operation instead of every 400 hours of operation. Any TLS/Bravo I fly will be compliant with the 400-hour interval! What happens if the exhaust valve guide has wear beyond the tolerances specified in Service Bulletin 388B, potentially catastrophic failure of an exhaust valve. Enough said!
• The Propeller and governor require overhaul every 5 years or 2000 hours since new or overhaul, whichever comes first. Also, and very important, ensure that the Governor has received the "T" modification. You can tell this by the serial number designation: it should resemble something like this C29003-D/T27. McCauley Propeller issued a Service Bulletin #202A which required substantial Governor maintenance. I have experienced one governor failure which did not have this modification performed. Luckily the landing was uneventful, however, thousands of dollars were spent for Engine/Propeller/governor overhaul!
• Carefully check the Propeller Spinner backing plate for cracks. I have seen a few TLS/Bravo backing plate's crack in the radius of the flange where the attaching hex head bolts attach. Check the metal engine mount for rust especially in the "wells" that the firewall attach points are located.
• Ensure that the engine isolator mounts are not sagging excessively. Mooney Aircraft Corporation requires replacement after 10 years in service.
• Check the oil inlet and outlet hoses at the turbocharger wastegate for chafing against the metal engine mount lower cross over tube. We once had to replace the metal engine mount due to excessive chafing from a wastegate hose. Mooney Aircraft Corporation recommends repair if more than 10% of the wall thickness has been damaged. That is not much metal folks!
• Check to ensure that the flexible fluid hoses have not exceeded their recommended useful life of 7 years.
• Check the thermostatic by-pass valve for compliance with Textron Lycoming Service Bulletin 518C.
• If either or both magnetos have more than 500 hours since new, ensure that they have received a 500 hour inspection since new or the preceding 500 hour inspection.
• Check the starter and starter ring gear for several chipped teeth. If maintenance personnel have not been paying attention, the starter drive and ring gear will be shot. P.S. Do not purchase and install the original starter it will just do the exact same thing. There are new starter alternatives for the TLS/Bravo that are vastly superior to the original equipment.
• Inspect the exhaust collector pipes at cylinders I & 2 for cracks, we have seen some of these pipes cracked in the field.
• Check the exhaust system for leaks at the cylinder flanges. Pay particular attention to cylinder #6. It tends to exhibit signs of exhaust gas by-pass more than the remaining 5 cylinders.
• Make sure the Stand-by vacuum pump drive inspection has been performed within the preceding 200 flight hours. We have seen some drives that are rounded off and will not pass the special inspection. I believe the cost of replacement exceeds $2,400.00.
  
  Now the Airframe:
  
  
• If the aircraft is equipped with a TKS system, ensure all airframe and windshield pumps are in good working order. We have experienced pump failures in the field. We believe the primary reason for failure is the lack of usage by the owner/operator! Also, because fluid comes out doesn't necessarily mean the pumps are operating properly, the operating pressure is critical.
• If an owner/operator is a heavy TKS user, inspect the bellcrank needle bearings in the empennage for rust. The TKS fluid seems to displace the lubricant applied to these components during service, allowing rust to occur.
• Carefully inspect the fuel tank area for leakage.
• Inspect the tail for excess play at the tail trim link mechanism. Also, check for excess play at the two hinge bolts.
• The two elevators and rudder utilize several rivets called, "Cherry Max" rivets. Inspect these rivets for sings of loosening. Occasionally, we have seen these rivets start to loosen or "work" as Technicians call it in the field. You can identify this by a trail of black soot aft of the rivets. Technicians in the field call this, "smoking rivets".
• Check the top sides of the wing flaps for excess chaffing. All Mooney wing flaps will chafe to a certain degree. However, if the flap attaching and actuating hardware is not maintained to near new tolerances, excess wing flap chaffing will occur.
• Check the landing gear shock disc's for excess compression. The maximum allowable compression is 5/8". Also, if you jack the aircraft and can rotate the shock disc's one half hour later, the shock disc's require replacement.
• Check the landing gear rigging and play amongst all of the actuating rod ends. If the aircraft was maintained by well meaning Technicians that are not very familiar with the TLS/Bravo landing gear system, there may be problems. Pay particular attention to the roll pins that are used to secure each rod end to its respective push pull tube. We note play in this area from time to time.
• Inspect the inboard landing gear doors where they attach to the round tubular structure for loose rivets. This requires jacking the aircraft and partially retracting the landing gear. If the landing gear is not rigged properly there is a good chance that these rivets are loose. I have seen twice in my career where the inboard landing gear door has exited the aircraft.
• Depending on the age of the TLS/Bravo, inspect the tubular structure for rust. On older aircraft that have received years of maintenance, tooling marks can scratch the corrosion resistant coating applied to the tubular structure at the factory. In the right environment, this allows rust to form and begin it's destructive path.
  

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!