For the pre-flight, in addition to the items in the manual, here are a few PA 31 tips:
- As mentioned above, just before the pre-flight in the cokpit, push the gear handle down, and pump the emergency gear handle a few times to lower the main gear doors. This checks the operation of the emergency pump.
- Check the main cabin door striker plates, and the actuation and security of the door handle - a weak point especially in older aircraft.
- On the engine, open the side access hatch and check for cracks of the exhaust pipe near the y-bend aft of the turbo charger.
- If the engine is cold! Check the security of the pipe itself (one came off in my hand one day, and a failure here will direct hot exhaust gas at the engine firewall). At night, you can see the exhaust glow red through the inspection port from the cockpit.
- Check the engine cowl security. The front of the cowl is held in place by two fairly short pins on the far left and right of the upper cowl. It is easy for these pins to be misaligned if the cowl has been removed and refitted, with the cowl appearing to be in place, it will depart the airframe in flight.
- Be careful when using the oil dipstick checking the oil to use the correct scale - the dipstick is marked on both sides, one side for the left engine and one for the right.
- If the fuel cap locks are stiff, a little oil dripped onto the lock hinge from the oil dipstick will free them up nicely
- Check the main gear down locks and the uplock hooks and rollers for freedom of movement. The uplock rollers can rust up, causing the gear to hang.
- Evidence of leaking fuel cells (bladder tanks) may be seen around the screws at the wing root fairing as a blue/green stain. If this is the case, fuel vapour will have collected in the wing root fairing, and may be ignited should a backfire occur on start causing an explosion. This has happened twice in Australia that I have heard of.
- Check the crossfeed on taxi out (you do anyway, don't you?) in order to remind you of the crossfeed procedure. Remember that the fuel pumps "belong" to the repective tank, not the engine, in that crossfeeding from the right tank to the left engine requires the right fuel pump to be on (not the left!)
A few operating tips:
- When you start the first engine, the hydraulic pump will operate, closing the main gear doors, and returning the gear handle to Down-Neutral. This checks the operation of the engine driven hydraulic pump. To check the pump on the other engine, either alternate the engine you use to start, or shutdown the engine you started first, push the gear handle down and watch it return to Down-Neutral (at 1200 RPM, the handle should return within three to nine seconds), then shut down the second engine.
A slow return to Down-Neutral of the gear handle may be an indication of a worn pump or an impending serious hydraulic leak.
- Landing on a muddy runway can throw mud up into the flaps,fouling the flap micro-switch located behind the gear (you can see it when the flaps are down). This will result in the flaps not being able to retract. Cleaning the area can solve the problem.
You may have to reset the flap circuit breaker in order to reset the flap time delay switch (the assymetric flap protection).
If all else fails, the flap relay is located in the cabin floor between the flaps - I once had to jump past the relay in order to retract the flaps and get home. Don't know that I would recommend that - but if you do, be careful not to overrun the flaps as the motor won't stop when the flaps are up!
- If you need ground power to start due to a flat battery (master and electrics off during start), remember that the battery relay requires battery power to close - so if the battery is flat, even though the aircraft is running and powered, the battery will not charge.
Before shutdown check that, with all electrics off and the engines at 1000 RPM, the ammeter is showing the battery charging at less than 25 amps in order for there to be enough power for the next start.
- It is possible to obtain an excessively rich mixture if continous flow fuel pumps are used at the same time as emergency (boost) pumps, although this shouldn't occur if the fuel control unti is correctly set.
- Many ammeters on these aircraft operate poorly, a good cross check of alternator voltage is to turn on the cockpit dome light and check for brightness.
- It is possible for the prop governor to freeze in icing conditions, if you use 2200 - 2300 RPM for cruise, your power will be limited by the Manifold Power restrictions.
- The left alternator belt can slip in moderate to heavy rain, causing a low voltage light.
- A leaking left cockpit window can allow water to drip into the CB panel, causing a total power failure - including battery power.
- The fuel consumption figures are a bit understated in the manual. so holding times and best economy fuel flow rates are only obtained at peak EGT, and sometimes not even then. Be conservative in planning fuel, and don't trust the manual's figures!
- The EGT pointer can stick, and a sudden drop in Manifold pressure may be a lose pointer - if these occur, look for a secondary indication (like yaw) before jumping to conclusions!
- Like all bigger Lycomings, the engine can be a lttle difficult to start when hot. The best technique I found was to close the throttles, hold the mixtures at idle cut off, and run the fuel pumps for five or six seconds to flush the lines with cold fuel, removing any vaporised fuel in the lines. (The fuel travels from the tank through to the engine to the fuel control unit, then returns to the tank as the mixture is at idle cut off.)Turn off the fuel pump, then move the mixture from cut off to full rich and back to cut off - you will see the fuel flow indicators jump a little as a small charge of fuel enters the cylinders.
Open the throttle a half inch or so and crank, if the engine doesn't start within two or three rotations keep cranking and open the throttle fully. It should start nearly immediatly.
As soon as it fires, increase the mixture to full rich and quickly close the throttle to idle.
Note: The above is from memory, and I haven't flown a Navajo for seven odd years, so take it all with a grain of salt, and ask your instructor!
Apart from that I like the aircraft. It is big and stable, good for IFR work and handles a load pretty well. Have fun!
[ 22 November 2001: Message edited by: Checkboard ]