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.