What to look for in a prebuy?

[ljmolina]

All, Im about to buy a 75 Pressurized T337G, I have a good list to check from people that I know who has flown skymasters... I do have a guy to help assist with a prebuy, but for my own knowledge and understanding Im hoping maybe you guys/gals could help on what to look for and add to my small list to check.

Thanks

[mshac]

Test the pressurization to be certain it can maintain max differential. If there are leaks, they can be expensive to find and fix.

If there is a recording engine monitor like a JPI, download the data and send it Savvy Aviation for analysis. They can really give insight into the health of the engines and individual cylinders.

Check for oil leaks on the rear engine. They are SUPER common.

Check the plane after sitting overnight or even better a few days to see if the gear doors start to droop down. If they do, your gear accumulator is bad. Its located under the floor near the pilot's seat.

Test the gas-fired heater and be certain its been inspected on schedule. Surprising to me how often this gets overlooked, especially in warm climates.

Check to see when alternator drive couplings were last changed. Mine had just been replaced at about 800 hours when I bought my P-model. They typically wear out before TBO. If they fail, they cause serious internal engine damage.

Test flight for fuel flows (are they matched?), throttle positions (are they aligned?), oil pressure/temps, make sure all gauges have correct indications. Check the AP for holding altitude and heading. Check the NAV function on both a VOR/ILS and a GPS fix (if coupled). Check the electrical system by turning off each alternator to be sure the other alternator picks up the load. Check to see if the alternator warning lights are blinking during flight (another very common scenario that my 400-series voltage regulator upgrade is designed to fix - $499).

Check fuel gauges for correct indications throughout the range - they are a known weak point in the Skymaster.

Be sure the powerpack is topped off with hydraulic fluid (its behind the center pedestal cover).

I'm sure I missed some things, but this is a start at least.

[ljmolina]

Thanks for the info! Im actually looking at buying one of our members plane if the prebuy goes well this Monday.. Its is Barry Sloane (N187) plane.

[ljmolina]

Here is what I have so far... Anyone, please feel free to add to list of known skymaster problematic areas or issues.


 FUEL LINE LEAKS
-Look for Obvious Fuel Line Leaks

 OIL LEAKS
-REAR ENGINE notoriously known for oil leaks.

 FULL FUEL CHECK
-If you fill the tanks too fast the inner tanks does not fill as quickly as
the outer tank and can cause you to lose up to 12 gals.

 MAG CHECK REPLACED?
-Mags are good for about 300-400 Hrs
-Are they Pressurized Mags?

 FUEL PUMPS - need clarification
-something about setting fuel pump to LOW and if the engine needs
more fuel pressure, they automatically go HIGH?

 ENGINE MOUNTS
-Check engine mounts (especially the rear)

 ALTERNATOR
-Check Alternator drive couplings for slippage. The wear out before
TBO, and can cause Internal Engine Damage.

 VACCUM PUMPS
-Most of the time they are 300 hrs pumps and need serviced.

 LANDING GEAR DOORS
-Check for gear door droop. If they do, the Gear Accumulator is bad
(located near under the pilot seat)
-Manually Cycle the Gear

 LANDING GEAR POWERPACK
-Top off with Hydraulic Fluid (behind center pedestal)


IN FLIGHT

 POWER ON TAKE-OFF
-Make sure the Power Red Lines on take-off

 JANITROL HEATER
-Verify functioning (Just replaced / refurbished)

 FUEL FLOWS
-Check that Fuel Flows Match

 THROTTLE POSITION
-Verify throttle positions are aligned

 GAUGES
-Make sure all gauges have correct readings.
-FUEL GAUGES ( Right Gauge was just replaced)
-OIL PRESSURE
-ENGINE TEMPERATURE

 ALTERNATOR FUNCTION
-Check each alternator
-Switch Front OFF (Verify the rear alternator picks up the load and
Warning Light) then, back ON
-Switch Rear OFF (Verify the front alternator picks up the load and
Warning Light) then, Back ON

 CABIN PRESSURE CHECK
-Take Plane upto 17,500 ft and ISOLATE each engine and check to see if
the cabin pressure can maintain max differential pressure (3.25psi)

 AUTO PILOT
-Verify Altitude HOLD
-Verify Heading HOLD

 NAVIGATION
-VERIFY VOR / ILS functionality

[mshac]

Originally Posted by ljmolina

 CABIN PRESSURE CHECK
-Take Plane upto 17,500 ft and ISOLATE each engine and check to see if
the cabin pressure can maintain max differential pressure (3.25psi)

You don't need to go to 17.5 to verify the pressurization system. You could do it at 8.5, just be sure the differential gauge on the pressurization control panel is at max.

That said, taking the plane to 17.5 will expose bootstrapping, weak mags, and weak wastegates/turbos. Its well worth it to fly that altitude during the prebuy if at all possible! If one engine can't hold manifold pressure or starts to miss up there, you know you have an issue.

These airplanes were designed to fly high. They are both faster and more efficient the higher they go. I find 17.5 to be a "sweet spot" on a lot of trips. You're VFR, but with flight following at that altitude, you get great service from controllers, almost as if you were an IFR flight. Also, there is very little traffic at that altitude. I'll go hours without ever seeing another aircraft sometimes. My father once complained that it was "boring" flying so high because he couldn't see anything, so I flew him from Nashville to Dallas at 2500 ft - he loved every minute of it! Kept me out of a strong headwind too

[ljmolina]

Thanks for all the info... Im kinda nervous and excited as this will be my first plane I own...the skymaster has always been my childhood dream plane...and now I can afford one...I hope it goes well Monday.

Luis