2010-06-23 21:44 | fche blog flying dive dive dive

Last night, I renewed my IFR privileges for another two years, after passing a flight test with my friend Charlie Rampulla. One mistake I made may be interesting reading for other pilots.

The mistake involves the VOR-DME-A approach into CNC3 (Brampton, Ontario). This is a non-precision circling approach. The airport is near hills and towers, so some step-down points are dictated, which best not be busted. Here is a copy of the approach plate:

The challenge here is not the simple following of the inbound track from the northwest. Unfortunately, that was the challenge I set my mind to, and missed the real one: vertical navigation.

The last stepdown fix, TIBIB, is 1.9 nm (3.5 km) from the airport edge, PEVGU. One starts at 2020 ft up, and one must descend to 1440 ft for the circling manoeuvre needed to line up with any of the runways. Once lined up (via the circling), one may descend the remaining 505 ft down to the airport’s 935 ft elevation.

At the speeds of GXRP, that TIBIB-PEVGU leg of 1.9 nm distance takes about one minute to cover, during which time it has to lose 580 ft. No big deal, right? Wrongo, as I found out. One does not actually have 1.9 nm to descend, but much less. This is because, in order to begin circling, one already has to have sight of the airport. If one pops out of the clouds exactly above the airport (1.9 nm later), it’s too late! One needs to see the runways at least 1 nm ahead of time, and preferably closer to the airspace radius protected for circling: 1.4 nm or so. (The approach plate suggests a visibility minimum of 1.5 nm too.)

That means that instead of 1.9 nm in which to descend 580 ft, one has only … 0.5-1 nm or so. That’s only 15-to-30 seconds of flying, which means a 2320-to-1160 ft/min descent rate! Whoa dude, elevator going DOWN! Unfortunately, I didn’t realize/calculate this ahead of time, and arrived to the circling altitude way too late. I barely salvaged a passing circling/final/landing. (The simulated failure of an engine during the exercise didn’t make it any easier or harder.)

So, lessons. Circling approaches can require getting to the final minimum altitude (1440 ft in this case) earlier than for a straight-in approach to a particular runway. Prepare for high-rate descents. Oh yes, and have fun.

UPDATE One should remember that even for straight-in non-precision approaches, high rates of descent may be required.

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The old chop and drop can make for a very unstable approach which can be very dangerous. Too bad they have to design non-precision approaches like that.
I just renewed my PPC in the sim last week. During the approach I noticed that the right engines oil pressure had dropped to a level that required that the torque be reduced by about half. The checklist was completed and the circling approach began. During the go around (ATC initiated) full power was applied as per the go around procedure. However I failed to remember that full power was now 2000 ft/lbs instead of 3950 ft/lbs. The engine subsequently failed. Oh the tangled webs we weave.
Flight tests are not only tests but a great opportunity to learn new lessons.
Nathan (Email) - 2010-10-12 22:08

I wonder how many PPC candidates are caught by the same thing.
When you did the go-around, were the power levers already split? Would’ve been your only reminder about the half-failure?
Frank - 2010-10-13 08:09

The levers were not split as that would result in asymmetric thrust. And with that much thrust (1279 horsepower) that could lead to problems. (it’s company culture to even them out).
The examiner was banking on it happening. He has to test an engine failure during the missed. So far everyone he has tested has done the exact same thing giving him the condition that must be covered during the test. He could manually fail the engine if the candidate does not raise the engine to max power but so far it has not happened. If I have him again next year he won’t catch me again.
Nathan (Email) - 2010-10-13 10:25

Neat, so you turn down the power on the good engine to match the bad one, to keep the left & right sides balanced? I wonder if the examiner is expressing his disapproval of that technique by his choice of this demonstration. Perhaps retaining a small split would be better than risking forgetting it.
Frank - 2010-10-13 10:30

  
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