Tuesday, September 27, 2005

Optional Procedure Turns

The most awkward part of a hockey stick procedure turn is transitioning from crossing the beacon, to tracking outbound along the shaft of the hockey stick. If you arrive via a heading that is close to the outbound heading, then you only have a small turn to make passing the beacon, and can line up quite easily. But if you are approaching the beacon from the inbound heading, you have to do a full 180, and then have to make quite a large cut to intercept the outbound track. It may be more convenient to use another form of procedure turn.

If you arrive at the beacon via a heading that is close to the inbound heading, the racetrack may be the easiest. After crossing the beacon, the pilot makes a turn towards the protected airspace side, to the outbound heading, and simply parallels the outbound track for a couple of minutes, before making a one-eighty in the same direction to interept the track. It's shaped like a hold. In still air, this should work out nicely, but with wind you might not end up where you think you are. One of the dangers is that with a strong wind blowing from the protected side, you could be blown through the track so that when you made your turn, you were actually turning away from both the inbound track, and the protected airspace. You must pay attention to the instrument indications of your position relative to the track, even though you aren't tracking. The wind could blow you sideways, pushing you towards the inbound track, so that when you turned around and tried to intercept it inbound, you would overshoot it during the turn. If that started to happen, you could intercept the track outbound and then switch to a hockey stick procedure turn. If you caught it early and really had your heart set on a racetrack, you could switch to a modified racetrack.

You might choose a modified racetrack if you were approaching from the unprotected side at an angle that might put the outbound leg of the racetrack too close to the inbound track. So crossing the beacon, you turn to a heading that is about forty-five degrees from the outbound heading, towards the protected side. You fly that heading for a minute, then turn to the outbound heading for a minute or two, and then turn 135 degrees, to intercept the inbound heading at 45 degrees, just like the corresponding part of the hockey stick PT.

Coming from the protected side, some pilots do an S-turn: crossing the beacon, turning immediately to a heading 45 degrees to the protected side of the outbound, flying that heading for a couple of minutes, then turning around to intercept the inbound. It's kind of like a modified racetrack for people arriving from the protected side.

There's also a 90-270 rapid reversal that starts out like the hockey stick, but instead of turning forty-five degrees off track and then doing a one-eighty, the pilot turns ninety degrees off track and then almost immediately whips the rest of the way around to intercept it. I suppose it's faster.

The hockey stick (or the faster varient) procedure turn does have one huge advantage, and that is that while flying outbound, you are tracking, following the needle indications that tell you that you are exactly on the outbound track, and not confusedly flying the wrong way, nor being blown by strong winds out of protected airspace and into a mountain. I favour the hockey stick or the racetrack. My philosophy is that if you have to cross through the outbound track anyway, you might as well intercept it.

I believe that in the United States (and someone will correct me if I'm wrong), this thing is called a course reversal, instead of a procedure turn, and you're only allowed to fly it as depicted on the plate, and those are usually hockey sticks. I doubt Americans do them much at all: radar coverage is almost universal in the States.

3 comments:

david said...

(You really need pictures for this one.)

As far as I know, Americans also say "procedure turn". While their radar coverage is pretty-much universal at altitude, it can be very spotty lower down, especially in hilly areas. I've been out of radar coverage even at 8,000+ feet flying IFR across both Maine and New Hampshire and had to fall back on no-radar reporting procedures, so I would very likely have had to fly a full procedure approach into an uncontrolled airport in those areas.

aasmodeus said...

Er... I'm still trying to digest that before I pull out my openoffice diagram template and try to ... er... omigod. I need to wake up before I even think about it.

Brought to you by the 'word' ayojmya, which I first mistyped as ayojimya, trying to make it a (still non-) word.

John said...

In the U.S., we call it a procedure turn. Many procedure turns are depicted as a barb (what you call a hockey stick), some are depicted as holds, some as tear drops. If the procedure turn is depicted as a barb, you can do whatever style turn you want, as long as you do it on the same side of the approach course as shown the instrument approach chart.

A commonly misunderstood concept is "procedure turn inbound" which is where you have completed the course reversal and are established on a segment of the approach. Many pilots think procedure turn inbound just means you've turned inbound.

To add to the interest (or to put some readers to sleep), US controllers never expect you to do a procedure turn when you are being vectored. To wit: "In the case of a radar vector to a final approach course or fix, a timed approach from a holding fix, or an approach for which the procedure specifies 'No PT,' no pilot may make a procedure turn unless cleared to do so by ATC."

And yes, there are still a fair number of places in the US where radar coverage is not provided.