VH-POM blog

Initial disassembly

On Monday (6th June) we drained several litres of water out of the left main fuel tank (it’s not exactly well-sealed and Murwillumbah got quite a bit of rain) and taxiied the plane to the hangar. First thing to do was a quick inspection of the main wing spar. Comanches have had some serious problems with wing spar corrosion, as a direct result of an Airworthiness Directive that required a drain valve fitted under the auxiliary tanks. Poor sealing around this valve resulted in engine exhaust entering the wing and corroding the main spar. A corroded main spar generally means that the aircraft is written-off; repairs are worth more than the plane. Shortly after these problems appearded, a second Airworthiness Directive was issued telling everyone to remove the drain valve and go back to Piper’s initial design.

Luckily, VH-POM only has minor surface corrosion here (as would be expected from any piece of aluminium that’s fifty years old and has spent a lot of time in Queensland). It should clean up well with a bit of bead-blasting, and then we can repaint it with corrosion-resistant paint.

With that done, we removed the nose cowl, which revealed the voltage regulators (upgraded, but still mechanical – no fancy electronics here!), paralleling relay (which only has one wire connected to it and therefore probably isn’t doing very much), heater (missing fuel control), and radar (mounted off-centre and hidden behind the standard fibreglass nose).

 

We then progressed to removing the fuel bladders. The Comanche’s two main tanks (30gal each) and two auxiliary tanks (15gal each) hold fuel in rubber bladders, which are clipped onto the inside of the wing. Mains are between the engines and fuselage, auxiliaries are under the engine nacelles and extending outwards. There are two very common fuel-related problems for Comanches. The first is that the nice bowl-shaped cutout in the wing around the fuel filler really likes to collect water. If the filler cap doesn’t seal perfectly, the cutout neatly funnels all this water straight into the fuel tank. The second problem is that the rubber bladders tend to go hard and brittle over time, especially if the plane is parked outside (as VH-POM has been for many years) without much fuel in them (fuel helps to keep them soft).

What we found was a huge amount of corrosion in the wing cutout for the left tank (the fuel level measurement system for that tank has just about rusted away), and an extremely old (built in 1968) bladder in the left auxiliary tank, but apart from that it’s all pretty good. The two right bladders and the left main bladder are all “new” (ie less than 20 years old) and all the other fuel senders look to be fairly new too.

With the fuel system largely under control (in that we know what it needs) we did a compression test on the engines. All looking good so far; compression was acceptable on all cylinders. We found evidence of significant (repaired) damage all over the inner-left part of the plane – patches added to the wing, doubler-plates on parts of the engine cowling, repairs to the propeller spinner, and the engine has been replaced not too long ago.

 

As a final point for the day we pulled off a bunch of inspection panels. The plan is that I’ll try my hand at touching-up some of these (ie removing corrosion, getting paint matched) and if I mess up too badly there are spares available. Photos of that to come.

After all that, we reassembled it, installed a spare panel to replace one that I’ve taken home, and called it a day.

Here’s a somewhat belated update on VH-POM.

I visited Murwillumbah on the 5th – 7th of June to have a look over the plane post-flight, do some initial maintenance, and talk to the avionics engineer about what needs to be done. They’d recently had a lot of rain, which resulted in people kite-surfing on the end of the runway…

VH-POM was there as expected:

Exterior looks fine, although the paint is pretty bad in places:

Generally the white paint seems pretty good; it’s the maroon that’s taken a beating.
First thing to do was to get a listing of the avionics that’s actually in there. This is:

Bendix-King KY-97A VHF radio – the standard VHF radio for light aircraft.

Collins VHF-251 VHF radio – was probably the standard VHF radio forty years ago, when it was reasonably modern (the only information I’ve found on this comes from an advertising brochure dated 1971)

Codan HF2000 HF radio – a decent HF radio, used when out of VHF range

Garmin GPS155 – a very old (as far as GPS goes) TSO C129 GPS. This means that it’s adequate for almost everything, except driving a new transponder.

Narco NAV-121 – a nice VHF Omnidirectional Ranging (VOR) receiver (aka “NAV”). Unfortunately a Airservices Australia has recently shut down most of the VOR transmitters. There are still a couple near big airpots (eg. Canberra has one) but they’re definitely fairly rare. Nice in that it all fits into a standard instrument slot, whereas many NAVs use two slots.

Narco NAV-122 – like the NAV-121, but it provides glideslope and marker beacon support as well.

Narco ADF-141 – a pretty ancient Automatic Direction Finder (ADF), but if it works it’ll do the job. Airservices shut down most of the NDBs (beacons that the ADF receives), but the ADF has an advantage over VORs because it can also receive (and navigate using) AM radio stations.

Bendix-King KN-62A – a nice example of a Distance Measuring Equipment (DME) transmitter/receiver. DMEs are in the same category as NDBs and VORs (ie largely obsolete), but there are still a couple around and it’ll be worth hanging onto this. Doesn’t currently work, so it’s been removed for repairs.

Narco AT-150 – an old transponder. Needs to be updated to meet the new rules (due February 2017).

Bendix-King RDR-160 – weather radar. This plane has it mounted off-centre in the nose, and it does not seem to work very well – I’m unsure whether it’s actually broken or just not set up right.

Stec System 50 autopilot – at least one thing in this plane is not obsolete! Still old, but autopilot technology hasn’t really come a long way since this was new. Word from the previous owner is that it doesn’t like the rain and only works when dry. Initial testing suggests that the servos are not engaging.

The plan is to keep what I can for now, and look at doing a significant panel update in the relatively near future. In particular, to remain IFR-compliant I need to install a Mode S transponder and a suitable (modern) GPS receiver.

Since VH-POM has now flown for the first time in almost two years, now seems like an appropriate time to start a blog about it.

This if VH-POM:

(photo from 31/10/2015, when I first had a look over it. It hasn’t changed much).

I bought VH-POM in December 2015. It was being offered at a very low price anyway (although still more than I could justify), but the owner was keen to sell and we were able to agree on a price that was practical for me. The downsides were that it hadn’t been flown for quite some time (since 04/07/2014), there was no current maintenance release, and it’s badly in need of an avionics update. The paint is also not doing too well, but this is par for the course on a plane that’s been sitting outside for years.

VH-POM is a “basic” PA-30 (not a later PA-30B, PA-30C, or PA-39). It’s number 114 off the production line, which may even make it the oldest Twin Comanche in Australia. It was built in 1963, which puts it closer to World War I than to today, and its Australian Certification of Airworthiness was issued by the Department of Civil Aviation on the 16th of December 1963.

Since I bought it, it’s been sitting at Caboolture (just north of Brisbane) awaiting maintenance. Yesterday, after agreement from the Civil Aviation Safety Authority (CASA), the Licensed Aircraft Maintenance Engineer (LAME) who has so far spent over forty hours working on it, and the ferry pilot, it was flown down to Murwillumbah where it’ll be prepared for further flying.

 

More to come, as the maintenance gets done…

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