Twin Comanche Pre-Purchase Checklist

 (Ken Mori)

This is a list of checklist items for doing a preliminary screening prior to doing a pre-purchase inspection. Research the appropriate logs and verbally discuss to determine status.

 Engine

 Refer to engine log books, journey logs and verbal.

 Number of hours since major overhaul. If majored, were new cylinder kits installed or were the cylinders field overhauled? What are the cylinder compression reading over the past five years? Are there trends?

1. How many annual flying hours in the previous 5 years.  If the aircraft has not flown many hours, there is a possibility of internal engine corrosion.
2. When were the mags last inspected? Mags are required to be inspected every 500 hrs.
3. Are the mags Bendix or Slick? Bendix mags were the OEM. Slick mags cause difficult starting problems when temperatures are 5 Deg C or below. The impulse coupling tends to stick and not release.
4. Starters.  Are they light weight? Light weight preferred because of improved starting energy, lighter weight and no clutch problems.
5. Generators or alternators? Alternators preferred. When was the alternator/generator belt replaced. Recommend belt replacement when prop overhaul is done every ten years. (Canadian Reg)
6. Hoses.  When were they replaced.  Recommended replacement every 5 years.
7. Lord mounts.  When were replaced? Recommended replacement every 12-15 years. If the engines are sagging, they need replacement.
8. Alternate air boxes. Are the hinges and shaft for the cover worn? Are there cracks in the corners of the boxes?
9. Are the fuel lines to each of the cylinders from the spider/fuel flow divider uncovered? If there are any black covering on these lines, they are required to be removed.
10. How easy is it to move the throttle, mixture and pitch levers? If they are stiff to move, the barrel collar on the engine side is bent (cannot see visually) and the cables need to be replaced. 
11. When were the turbos were last overhauled. Need a flight test to determine whether they are leaking or not.
12. the little short lengths of hose right next to crank case that return oil from the valve covers to the sump should also be checked and replaced.

 Propellers

 Refer to prop logs. In Canada, the props must overhauled every 10 years or as per Hartzell  SB, which ever comes first. For most private flyers, the 10 year time limit comes first. In the US, the regulations are different.

 When were the props and governors last overhauled? In Canada, props must be overhauled every 10 years or 1200 hrs, whichever comes first. Prop governors overhauled at engine overhaul. Main concern is corrosion of the prop hub internals.

1. Were there any prop strikes?  If so, how was it repaired. Was an engine teardown inspection done?
2. Prop spinners.  Are there cracks radiating from the spinner screws? No repairs via patches are permitted. Prop spinner must be replaced.

 Landing Gear

 Refer to Journey logs and AD/SB listing

 When was the 1000 hr gear inspection done in compliance with AD 77-13-21 and SL782B? Bushing, bolts and thread wear must be measured to ensure compliance with design tolerances and to prevent gear collapses.

1. When was the side brace stud inspection done in compliance with AD 97-01-01R which requires NDT for cracks.
2. When was the landing gears serviced for replacement of ‘O’ rings, wiper and hydraulic fluid. Recommended servicing every 5 years.
3. When was the landing gear transmission last serviced.  Recommended service is 500 hours.  Was the proper grease used?
4. When was the bungee cord replaced.  Recommended replacement is every 3 years or 500 hours.
5. Was the landing gear conduit replaced? If they are original, they are over 50 years old and should be replaced.
6. Was the landing gear microswitches and harness replaced.  Again, these are old and the wiring has probably become brittle and prone to failure, and the microswitches can absorb moisture causing it not operate.  Both failures cause the green light to fail to come on when the gear is down. If not replaced, recommend replacement asap.
7. Brake disc. Check wear limits on the brake disc and disc pads.
8. Landing gear door.  Are they loose? How do the doors fit with the gear in the up position? Is it rigged properly? Are there any interference with wiring harness for the microswitches and the airframe? Same for the hydraulic brake hose.
9. Tires and tubes. What kind of condition are they in? If the main tires show uneven wear(ie wearing more on the inside or outside), it means the a gear alignment is required.
10. With the aircraft on jacks, check the pressure on the over centre position of the main gear drag links by pushing it up out of the over centre position. If you can move it, the gear bushings/bolts/drag link threads are worn beyond limits.
11. Nose gear turn limit stops.  Are these stops sheared? Are the turn limits well marked? If the stops are sheared, there could be other consequential damages such as stretched cables, over stressed nose gear housing, etc.
12. Main landing gear trunnion. Look for hydraulic fluid (red color) seepage near hole in web for clamp. If the airframe has between 4500-6000 hrs, there is a possibility of the trunnion to crack at this point due to poor manufacturing that left stress raisers on the web.

 Airframe General

 Refer to journey log, AD/SB listing.

 Flap tracks and flap track rollers.  Have the flap tracks been replaced, especially the outboard track. They tend to wear a grove and could result in an asymmetric flap deployment. This wear condition can be detected by holding the outboard end of the flaps while in the up position, and checking for up and down movement. Any movement indicates worn flap tracks. Have the flap rollers been replaced with nylon rollers?  If not, they should be replaced because the original steel rollers tend to wear the flap tracks quickly.

1. Rudder gap seal.  The original gap seal are rubber and due to age, most have deteriorated. The only replacement is a gap seal strip from Knot 2U. The purpose of the gap seal is to prevent air from passing through the gap to provide more rudder authority during single engine operation.
2. Torque tube and stabilizer inspection in compliance with SBs 1160 and 1189. Was this done? This was issued to determine cracks in the torque tube stabilizers and the stabilator horn.
3. Janitrol heater.  When was it last overhauled? The combustion motor commutator ring tend to wear a grove by the brushes and causes the motor rpm to slow. This in turn, causes the heater to operate on the rich side which shows as black streaks from the heater exhaust. These heaters must be pressure decay tested every two years as per AD 2004-21-05 to inspect for combustion vessel cracks.
4. Windows.  Are they crazed or discoloured?
5. Window trims.  Are these plastic trims cracked and faded?
6. Seats, side panels, headliner and carpeting. Are they worn and require replacement?
7. Are there built-in intercoms for the passengers?
8. Fuel cells.  If they are older than 15 years and there is smell of fuel in the cabin, it is highly likely that the fuel cells need replacement.
9. Fuel selector valves.  Have these been overhauled within the last 5 years? If not, there is probably corrosion in the valves. Have the microswitches and harness mounted on the fuel selector valves been replaced?
10. Exhaust heat shield. If the liner has deteriorated, they require replacement. The fuel cells are located above these heat shields.

 Avionics/Instrument Panel

 Preliminary nav/com equipment checks can be done on the ground but a thorough check is recommended by conducting a test flight, especially the autopilot operation.

1. Vacuum gyros. When were they last overhauled? Recommend 500 hours between overhaul, especially if they provide input to the autopilot. Are there records showing how often the vacuum related filters have been replaced.
2. Static test.  This is required to be done every 2 years.
3. Transponder/ altimeter correspondence check/recertification.  Done every 2 years.
4. ELT. Recertification required annually
5. Autopilot. Digital or analog. If analog, and the navigators are digital, there may be interface problems Similarly, if the autopilot is digital and driven by analog navigators. They may not “play” well each other. Look for digital equipment. Analog equipment is becoming obsolete.

Partial List of Important AWDs and SBs

 AD 74-16-08. Inspection for cracks in the area of aft fin attachment bracket. Repetitive 100 hr unless kit 760-783 (Stablilator bracket kit) installed.

1. AD 79-20-10. Aileron nose rib inspection for cracks. Repetitive 100 hr unless kit 760-893 installed. This supercedes AD 74-10-03.
2. AD 83-10-01. Fuel bowl inspection. Repetitive. 100 hr. Easily done at annuals. Inspect fuel bowl for corrosion and retention of water contamination..
3. AD 97-01-01. Side brace stud non destructive inspection for cracks at 1000 hr. Done with AD 77-13-21 and SL782B. 1000 hr gear inspection to ensure gear wear limits.
4. AD 77-13-21. Prevent collapse of landing gear after manual extension. See above.
5. AD 94-13-01. Inspection of stabilator torque tube bearing support for looseness.   Supercedes AD 74-13-01. Repetitive 100 hrs unless kit 760-835 (Hi-Shear Rivet Replacement) or equivalent compliance done.
6. AD 2004-21-05. Janitrol heater pressure decay test. Every 2 years or 500 hrs whichever comes first.
7. AD 2005-25-16R1. Prevent failure of fuel regular shut-off valve for Janitrol heaters. Pressure test for leakage. Repetitive.
8. SB 1160. Stabilator torque tube inspection for corrosion.
9. . SB 1189. Stabilator horn assembly inspection for cracks. This is an AD for single Comanches.
10. SL782A. Nose gear down lock spring installation. Kit 761-082. There should be 2 springs on the nose gear.

For Canadian registered aircrafts, to determine status of these AWDs/SBs, refer to the aircraft technical log, section 1, Airframe and section 2, Record of Installations and Modifications to Aircraft.

 Most engine and prop AWDs/SBs/Sls should have been addressed at engine and prop overhauls.

 Important regular maintenance items are:

 Landing gear transmission and flap transmission. Inspect and replace grease (important to use properly specified grease Dukes lubricant #4) in transmission housing every 500 hrs. Refer to Comanche Gear website.

1. Replace bungee cord every 3 years or 500 hrs.  Some recommend replacing every year.
2. Alternator brushes.  When were they last inspected for wear? Recommend inspection be done at annuals every 2 years.
3. Janitrol heater motor brushes. When were they last inspected. Recommend inspection be done at annuals every 2 years in conjunction with the heater pressure decay test.