In Response to Kevin Ware’s “Under Pressure” (November)
I enjoyed your article this month on pressurization. I just bought my first pressurized aircraft, a P337H Skymaster. I found your comment humorous, “I am routinely told flying piston twins without full pressurization is somewhat common in the industry” – as all I’ve ever flown for 25 years (besides airliners) is unpressurized twins!
You can fly a Turbo Skymaster (non-pressurized version) legally to FL300 while wearing an oxygen mask, but my pressurized edition with the same engines and very similar weight may only be legally flown to FL200 while pressurized. The cabin is at 10k when the aircraft is at FL200. I’ve read reports of owners flying as high as FL240 without issues, but I would imagine Cessna was trying to protect the pressure vessel when they limited it to FL200.
The Skymaster was the only twin ever built at Cessna’s Pawnee factory and one of only two pressurized aircraft built there – the P337 and the P210. So not a lot of pressurization experience at the plant. That said, I love the concept of being pressurized. On the inaugural flight home, I flew VFR at 17.5, and she maintained the max cabin differential the whole flight. From CO to TX, we averaged 210 knots and 24 gph total.
I appreciate you pointing out the deficiencies in the design, i.e., the inspection plate. So many times I’ve asked myself, “Why did they build it this way???” I know the day will come when I’ll be hunting down leaks in my bird, so I wish you the best with yours! May your leaks be sealed!
Enjoyed your article on the pressurization issue. I have a 1976 414 and every year mine gets a little worse. I have had mechanics chase this for several years without much benefit and a lot of money. My annual has just started, and I am interested in pursuing the cause during the inspection. My mechanic admits he comes short when it comes to the pressurization system but is willing to have me help him. Did you use the vacuum process and did you find your main leak? I have replaced many seals and boots over the years. On the ground, do you pull the gear breaker to bypass the squat switch that would open the dump valve? Any information would be greatly appreciated.