Pre-buy Inspection - Part 2

Aircraft Examination

ShopTalk - January 2018

by Kerry McIntyre

This month’s ShopTalk ... Aircraft Examination, completes our discussion about the pre-buy inspection. Before beginning to look at the aircraft, the aircraft logbooks should have been examined and any discrepancies resolved as per my previous article, Pre-buy Inspection – Part 1, Logbook Entries. You should have the service schedule filled out and have notes of what to particularly focus on during examination of the airplane.

One must understand that every seller will tell you his/ her plane is perfect, but our job at the pre-buy is not to prove them wrong but to expose the discrepancies to both parties and explain the cost for repair and the reason for the items found to be fixed.

A good example of this is the age and condition of the landing gear rubber shock discs. If these items are old, sacked out or hard as a rock, then during every landing the impact is being transmitted along the wing spar, flexing the structure and the fuel tank sealant. Eventually, this will lead to leaking fuel tanks and an MPI, a “Money Pit Item”. A typical repair to one tank can easily cost $2,500. If a complete strip and reseal is needed, it can exceed $6,000 per tank.

Starting with a clean notepad, sit in the pilot’s seat and write down every avionics and optional items that are installed. This includes speed mods, interior mods like aftermarket sun visors, engine gauges, and other items the plane did not come with new from the factory. A good example of this would be if you are looking at a 1965 M20E and it has a shoulder harness for all four seats. This model never came with shoulder harness restraint systems, but Mooney has a drawing for front shoulder harness restraints. The question is, “Are there any return-to-service documents for all four seats in the aircraft records?” We will look at everything installed on this pre‑buy plane with that outlook. Also, write down the tach or Hobbs time to compare later to your notes from the logbooks.

Run the engine until temperatures stabilize. From outside, examine how the spinner aligns with the cowling. Misalignment may be a hint of failed engine mounts. Remove the top and bottom cowlings and do a hot compression test. Record the results. Examine the engine for oil leaks, the condition of the ignition harness, the condition of the accessories and the wear on the spark plugs you removed for the compression test. Drain and discard a cup of hot oil and then drain more for a sample to send off for testing. I rarely remove and cut open an oil filter, the oil sample will be much more accurate. One of the conditions for the sale is a clean oil sample.

Look at the condition of the engine data plate and write down the model and serial number of the engine. Compare these to the logbook so you know this is the engine that you obtained all the data on. The model and serial number may seem like simple things to assume are correct, but I have seen engines come in missing their data plate, a serious MPI. Remember, we are not doing an annual, just looking at all the MPI items so our new owner won’t be surprised at the first annual.

The exhaust system – non-turbocharged: Look into the muffler for the condition of the flame tubes. Verify they are intact and not broken or warped. Examine the tailpipe support strap(s), ensure they are not broken and that the attach flanges to the cylinder have no cracks and missing nuts. If the exhaust system has slip joint or ball joints verify these are in good condition, look for exhaust dust as this can be a sign of a crack or leak in the system.

The exhaust system – turbocharged: Remove the air intake and examine the compressor impeller for nicks or rubbing on the housing. Look at the condition of the engine air filter and the integrity of the intake system, especially holes or leaks where dirt could get past the filter and damage the compressor wheel. Look for blisters on the bottom of the exhaust pipes and cracks where the pipes join or are welded together. I hook up a vacuum to the tailpipe running in blower mode and pressurize the exhaust. Then I spray soapy water on the exhaust looking for cracks of leaks. Look at the condition and security of all the V‑band clamps that hold the exhaust system together and the tailpipe on. An important check is to physically grab the tailpipe to verify it is not loose. Look for signs of excessive exhaust dust in the cowling and any blisters in the paint on the cowling. This can be a sign of excessive high TIT operations.

One final item for both types of engines is the condition of the heater hose and the outer can on the muffler. If these items have holes in them it is possible for carbon monoxide to leak into the cabin. Not a good thing for the occupants.

Remove the spinner from the propeller and examine the hub and blades for leaks. Look at the blades for any big divots that may have been filed out and blended in. This will throw the balance way out and may be cause for the blade to need replacing. If it has prop deice, check that both inner and outer elements heat up on each boot and that the boots are not cracked, rotten or delaminated. Look for wear on the deice brushes. These brushes are now over $100 each. Grasp each blade tip and verify it is tight in the hub by moving fore and aft. Last but not least, note the serial number on the prop hub and compare it to the logbooks. If the serial number is different, then the prop has been changed without a proper logbook entry, a violation of FAR 43. This could also be a clue to the condition of the engine, maybe an unrecorded prop strike?

So far, we have looked at the condition of the engine, accessories, and prop. Time to move on to the airframe.

Look over the outside of the plane for things like hail damage, Bondo patches, mismatched skin laps, even skins installed incorrectly. I have seen all of these and guess what? Not one of these items will have a logbook entry. Why? Because they were not done to the correct FAA standards.

On a Mooney, put the plane on jacks with the nose wheel off the ground. Lock up the rudder pedals and ailerons in the neutral position. Remove the belly panel(s) and check that both aileron/rudder interconnect springs are stretched equally 4.9 inches.

AD 98-24-11 required all Mooney aircraft built before 1998 to have gusset aileron link rods. When mechanics would change these per the AD requirements it was not uncommon to screw up the rigging. I could go on and on about all the ways I have seen this done. Just check it, because if it is off there is a good chance the entire plane is out of rig. Look at the rudder, it should be 1 degree to the right. Level the elevators, they should both match the stabilizer, not one down and one level. The ailerons should line up with the wing tips (if installed) and the flaps. Commonly, as various mechanics try to get the plane to fly straight and true, they will just mess with another control surface or flap in a vain attempt to solve the problem. If we find any clue the plane is out of rig then we will do a complete rigging check using all the Mooney travel boards and a digital protractor and document everything we find. This one item can add another hour to the pre-buy process. A MOONEY OUT-OF-RIG IS ONE OF MY PET PEEVES.

Open some wing and tail panels to look at the condition of the aluminum for surface corrosion. All airplanes (except new ones) will have some form of fuzziness or dull looking aluminum, but if the skin is pitted, we should look deeper into the overall condition. With the belly removed, search the tubular airframe for corrosion. Look carefully at the truss that the gear rods go through as this truss is almost always ground down during a gear up landing. Look for fuel tank leaks and note any old fuel stains you see.

Using the proper Mooney tools, measure the gear-down lock tensions to ensure they meet Mooney specifications. Try to rotate the landing gear shock discs and write down the date of manufacture listed on each disc. I have seen one new shock disc installed with three 25‑year‑old ones just to make it look like they are all OK. Make sure these rubber shock discs are not split or badly cracked.

Look at the condition of the brake discs and pads. It is not uncommon to see a dished out disc and there are limits. Look for oil leaking out of the brake caliper as well as the master cylinders under the floor. Check the parking brake valve for leaks. Lastly, check the brake fluid level.

If the plane has hydraulic flaps, look for leaks on the master cylinder. Parts for these cylinders are getting hard to find. However, electric flaps may be retrofitted, but this is another MPI. Make sure the plane has the correct ply tires installed as this is also part of the shock absorption system along with the rubber shock discs and proper tire pressure.

Run the gear up and check that the gear doors fit tight in the forward portion of the doors; we do not want anything hanging out into the airstream. If the plane has manual gear, look in the down‑lock block for an egged out hole or a lip cut into the hole where the Johnson bar fits in the gear‑down position. You will need a mirror and bright light and the gear in the up position. This is rarely looked at by most mechanics. Just because something is not in the service manual does not mean it can be overlooked. Listen for the aural gear warning.

If the plane has electric gear make sure all ADs are complied with along with the respective parts of the AD and when they are due again. If the plane had a new no‑back‑spring installed, note when (date and Hobbs time) so you can research if it had a recalled spring installed. Service bulletin M20-282 and its revised editions should be reviewed to understand the issue and determine if further action is needed.

We here at KNR-INC are not big believers in replacing this spring every 1000 hrs just because Eaton and Mooney say so. Most Mooney’s will get 2 gear cycles every 2-4 hrs as they are typically used for cross-country flights. If the airplane is mostly used to practice landings, then this no‑back‑spring item is very important. Mooney never built any TLS/Bravo or TN trainers.

Look for slop in the gear retraction linkage and do an emergency gear extension. Make sure the floor light that shows gear down works. I see these all the time inoperative. Check the slop in the nose gear steering horn as this is a common underserviced item and an important item to grease every 100 hrs or at every annual. These steering horns are shimmed to fit each airplane. If the nose gear is ever removed, this horn should be shimmed properly during re-installation. It used to be one could buy a new horn or the shaft that rides in the horn. If it is worn beyond limits, you must now buy the entire part for well over $1,000.

Look at the back side of the nose gear upper truss for dents in the tubes and broken-off steering stops. A new nose gear truss is another big ticket item to replace and if the steering horn is also shot one can blow through $5,000 trying to fix these items. Just another big MPI any new buyer will not be happy about.

Make sure the shock discs are not cracked and ask how the plane handles during landing. If the pilot that flew it in says it’s a little squirrely there is a good chance the nose gear rake and trail are not correct. On 1960s planes Mooney had a kit to solve this problem and often the extra collar on the nose gear shock disc shaft is missing. On later planes, Mooney drilled the attach bolt hole off‑center on this collar and it’s frequently installed upside down. All of these items can cause the plane to be squirrely at high speeds such as touch down. This may seem like a trivial issue, but when you run off the runway on landing and into the ditch that rips off the landing gear, you will realize this is an important item (especially if you do not have shoulder harness).

One last gear item: On the 60s and 70s planes, look at how much slop is in the nose gear fore and aft. The entire gear swivels on a long vertical bushing and bolt and it’s often necessary to install an oversize bushing and new bolt in this area. The parts are not expensive but the labor to pull the nose gear out is where it will add up and become another MPI.

Look at the condition of the interior and windows. If the plane has a new interior look for burn certifications for that interior (this is a FAR requirement). If it has thicker than normal windows, or 201 mods on older planes (60s and 70s), look for the proper STC and 337 forms for that work.

If the plane has a newer paint job, look for the log entry that shows the control surfaces were properly balanced or balance-verified per Mooney specs.

If the plane has a built-in O2 system, verify the manufacturing date on the O2 bottle. Remember life limit is 23 years for 3ht bottles and 15 years for composite bottles. 3ht and composite bottles manufactured before 7/1/2006 require a 3-year hydrostatic test. Composite bottles manufactured later require a 5-year hydrostatic test.

Look at the condition of the battery box and battery/ cables for corrosion. Write down the type of ELT and the battery due date. We often see ELTs installed in planes different from the one listed on the equipment list.

Grasp the horizontal stabilizer and move it fore and aft, there should be no noticeable play in it. Grasp the base of the rudder and lift it up and down, there should be some play in this motion. Once in a blue moon, we will find one that is tight in the up and down motion and this is OK also. Don’t panic over some free play in the up and down motion of the tail.

Check all the lights and stall warning horn for proper operation. Look for any unapproved lights installed on the plane. Some LED lights are approved for certified planes but many are not. Remember we are trying to verify the plane meets its type certificate data sheet and that any modifications do not compromise airworthiness.

So now sit down and compare the items you wrote down that are installed in or on the plane. At each annual, the equipment list and weight and balance are airworthiness items that must match and correctly reflect installed items. Lastly, check that all ADs are up to date and complied with.

On a typical Mooney, this Aircraft Examination will take 4-6 hours to complete. It is not an annual and there is no sign‑off for a pre-buy inspection unless there are repairs. Put the plane back together and let the pilot take the plane home unless the buyer and seller have made other arrangements. Remember, the mechanic does not determine airworthiness, we are just advisors. The pilot must determine airworthiness before each flight as per FAR 91.

Now, compile one list of airworthiness items and another of other discrepancies. At KNR, we typically do a repair estimate for each list. The buyer can then use the airworthiness items and the cost of repairs to negotiate with the seller. The buyer will also now know what other items may eventually need attention.

I hope these two articles will shed a little light on the mystery of doing a pre-buy inspection on a Mooney, or any other airplane for that matter. As always, if you have a question about this or any ShopTalk article, you may contact me at our aircraft repair facility by the old‑fashioned telephone: 307-789-6866 or by e-mail. Until the next ShopTalk, enjoy flying your Mooney. KNR e mail