Friday, July 08, 2005

Procedure vs. Technique

As I've previously noted, the modern airline expects its pilots to know and follow the published procedures for the airplane they fly. There is little use for mavericks that do it "their way." This lesson has been learned the hard way, through wrecked airplanes and lost lives. Everybody recognizes that there's more than one way to fly an airplane, but flying "by the book" keeps everyone on the same page and prevents crews from inadverdently becoming test pilots. Doing so is not as restrictive as you might think; there is a lot of leeway given for individual technique. Here's an example of how "by the book" pilots can use widely varying techniques, even while adhering to the letter of the procedures.

At my airline, each airplane has published profiles that will normally be followed when flying an approach in instrument conditions. For example: when flying an ILS in my airplane, you should be at 170 kts and Flaps 5 when joining the localizer; crossing the outer marker, you should be gear down and Flaps 15. Landing flaps must be set by 1000 feet above ground level (AGL). When in visual conditions, the requirements are considerably looser: landing flaps should be called for by 1000 feet AGL, and by 500 feet the airline should be at final approach speed (Vref) with the landing checklist complete. How one meets these requirements can vary from person to person and situation to situation.

Down low, my airplane is very flexible. With 50% torque, you can tool around at redline (245 kts below 8000'), but when you need to slow down, moving the power levers to flight idle will add a lot of drag. High gear and flap extention speeds mean that you can go from 245 knots to 120 knots (landing configuration) in a very short distance - if you keep the airplane level. No jet can do that. They have less drag, so they require early slowing if you want a stabilized approach.

One of my techniques for long visual approaches is to keep the speed at 240 kts while descending to pattern altitude early, in order to intercept the glidepath from below. When about 3 miles from glidepath intercept, I'll go to flight idle. By the time I've intercepted the glidepath, I'm at 200 kts and can go Flaps 5/Gear Down. Following the flap schedule, I'll call for landing flaps by 1000 feet and be at Vref before 500 feet, at which point I bring the power levers back up to maintain Vref. It's a slick technique that will smoke a 737 or MD80, but can only be used under the proper conditions. You wouldn't want to get below glidepath when wake turbulence is a factor. Speeding up on traffic ahead of you is a bad idea. Actually blowing by a 737 that's approaching a parallel runway will get ATC hopping mad at most airports (it's okay at SMF, though!).

The other day we were running late into Seattle. When approach cleared us for the visual approach we were 20 miles out and number one for the runway. I used the above technique, minding a crossing restriction over Boeing Field. I'd just decided to bring the power levers to idle when the captain growled "I wouldn't be this fast at this point!" He'd been tensing up as I got closer to the airport. After we parked at the gate, I apologized for making him nervous. He said he didn't mind, it was just the first time I had used that technique in front of him and he wasn't sure if I really knew how fast I was going. This captain usually descended on the glideslope, slowing gradually from about 15 miles out. If wake turbulence was a factor, that'd be how I'd do it, too. Under the actual conditions, the FSM contained enough leeway for both techniques to be acceptable. That said, it's important that the captain be comfortable with what his FO is doing, and the FO should adapt his flying accordingly.

1 Comments:

Blogger John said...

Sam,

Nice post! Interesting description of your visual approach technique as well as being sensitive to your captain's perspective.

10:58 AM  

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