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inquiry from Oakland Center Controller about our altitude changes. But luckily our brief deviation must have occurred between radar sweeps because the frequency remains silent and we, now both fully alert, fly on into the night with the autopilot on and my left hand guarding the control wheel. Though the controller might not have noticed, and the PM is an understanding guy, I made more than one mistake in this scenario. My response to whatever caused the altitude change took too long. Plus, I should have spent less time looking at the FMS/AP switches, or maybe had the PM do that while I just flew the airplane by hand. I won’t let that happen again.
A couple of months later, we are returning to our base airport at night in marginal IFR weather. We are set up for the RNAV/GPS approach on radar vectors to intercept the approach path and holding 4,100 feet as assigned by the controller. He says we are cleared for the approach, hold heading 030 and 4,100 feet until over SOCLO (the IAF) and established on the final approach course. With that, I push the APP (ap- proach) button on the Lear’s autopilot and am looking at the approach plate on my iPad when I hear the PM politely say, “I think we are supposed to be at 4,100 feet.” I look up to see we are down to 3,900 feet which happens to be the appropriate altitude for that position on the approach, but not the one assigned by the controller. Not sure what caused this to happen (and remembering the prior altitude event), I quickly switch off the autopilot and climb back to 4,100 feet hoping the approach controller did not notice. But this was not the case this time. He shortly says, NXX, “Say altitude” to which the PM truthfully replies, “4,100 feet and uh, we just had a slight auto- pilot malfunction which we have cor- rected.” The controller kindly replies, “Not a problem.” My mistake, of course, is that I know autopilots can do unex- pected things sometimes, particularly down low, and I should have caught the 200-foot altitude change earlier.
Fast forward to another night flight.
I am making the same RNAV/GPS approach in marginal VFR conditions in the Lear. The airplane is coupled to
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Jet Journal April 2019 / TWIN & TURBINE • 31