Wednesday, October 1, 2008

Looking in the Wrong Direction

My student and I were approaching Pocatello, Idaho, for some touch-and-goes with the tower. He is presolo. He tuned the tower in time to an interesting dialog. The weather was clear with visibility 10.

TOWER: "SkyWest 24W, we have a disabled aircraft on runway 21, can you accept runway 35?"

SKYW 24W: [after a short pause] "Sorry, no, we aren't authorized runway 35." That's not unusual; SkyWest operates under Part 121, which requires lots of runway analysis and the like.

TOWER: "SkyWest 24W, roger, hold over Pocatello VOR, maintain 6500."

You can see what happened on FlightAware, the best aircraft tracking site. The jet was
on downwind for runway 21, overflew the runway, and headed to the VOR. But this is where it gets interesting.

First, Pocatello is a VFR tower, and I imagine that they informed Salt Lake Center. Radar coverage is spotty and too far from the antenna; the tower does not have a BRITE display. I imagine...

Second, it was not a proper holding clearance. I assumed that it meant "hold as published," and was looking for the jet to the west of the VOR. The charted hold is "hold west on the 269 radial, left turns." I assumed...

Third, the jet got to the VOR and made a direct entry. They assumed that the AIM advice that in the absence of further holding instructions they should make a direct entry applied. They assumed...

Fourth, as we entered downwind at 5500 MSL, the RJ passed directly over us at 6500. Where did they come from? This is legal separation between a VFR and an IFR, but it was a surprise. I asked the tower ("What holding pattern is that RJ flying? I thought they'd be on the 269 radial."), but he did not sound surprised. So if he knew where they were why hadn't he called us as traffic for them and vice-versa?

And so I conclude: Everyone was wrong.

Tower: Did not issue a proper holding clearance, which should have been "hold as published," or maybe "hold northeast on the 030 degree radial." See the Aeronautical Information Manual, 5-3-7b. Tower did not inform converging traffic (altitude separated though we were, although he had no way of knowing that.)

Me: Did not catch the improper clearance, and assumed it was"hold as published." Looked for the RJ west of the airport, when actually it was northwest through west.

SkyWest 24W: Took lack of proper clearance to mean "enter a standard pattern on the course on which the aircraft approached the fix," to quote AIM 5-3-7c. But that applies if unable to get holding instructions. [I admit that I am mind-reading here, but would prefer to give the RJ crew the benefit of the doubt as far as regulations go the alternative being that they just made it up as they went along.)

Instrument regulations are maddeningly subtle. Important things are buried in the same banal prose as unimportant things. For example, are you required to have a visual descent point (VDP) on an instrument approach? (A VDP is the point on the approach after which a normal descent is impossible.) The regulations do not say directly that you do, but according to 14CFR91.175 "Operations below Minimum Descent Altitude" you need to have a descent rate that would allow touchdown in the touchdown zone if you are operating under part 135 or 121. In other words, a part 135 regulation is only listed under part 91. And this appears in the same bureaucratic prose as "truth in lending." There are many blank areas of interpretation to jump, lots of blank areas that do not seem to matter much, and little guidance on how to decide whether or how to jump them.

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