Insights

Why Timing Matters

For instrument flight, FAR 91.205 states that aircraft must have a clock displaying hours, minutes, and seconds with a sweep-second pointer or a digital presentation. Time is obviously important, but do you take full advantage of this cockpit resource?

I asked 20 instrument-rated pilots how they use the aircraft's clock, and the 20 responses were exactly what I expected: determining groundspeed, timing nonprecision instrument approaches, and keeping track of estimated arrival times and fuel consumption. They should have included cockpit management and course intercepts-two tasks that are simplified when time is referenced.

When I look at a terminal area's radio facility chart or an approach chart with feeder routes, I never see mileage. Yes, it is published next to each route segment, but when I see that number, I only see time. And when I think in terms of time, cockpit management becomes more relaxed and more efficient, particularly during periods of high workload.

To achieve this performance level, you must know the winds aloft, and believe me, pilots who take off without knowing the huff-and-puff forecast commit a serious error. When you know the estimated wind direction and velocity, you can quickly make a rough determination of groundspeed-in miles per minute-and begin thinking in terms of time rather than distance.

For example, the forecast winds are 270 degrees at 20 knots, and indicated airspeed is 125 kt at 5,000 feet, the cruise altitude. I use the 2-percent rule to estimate true airspeed (TAS)-it increases 2 percent for every 1,000 feet above sea level. In this case it would be 10 percent higher than indicated airspeed, or 137 kt.

A 20-kt headwind decreases groundspeed to about 120 kt, which is two miles per minute, and a 20-kt tailwind increases groundspeed to about 160 kt, which is slightly better than two and one-half miles per minute. A quartering wind yields intermediate values, and a direct crosswind yields a groundspeed that is several knots below TAS, a correction that can be ignored in this case.

If the next route segment depicts 14 nautical miles, I see seven minutes if flying with a direct headwind (14 divided by 2), six minutes if flying with a direct tailwind. I know exactly what I can accomplish in this time interval, whereas 14 miles doesn't mean much.

This type of thinking works in all aircraft, and it always gives you a quick idea of the time that is available. Cockpit management now becomes more efficient, and you avoid the perils of getting mentally behind or too far ahead of the airplane, situations that inevitably cause pilots to lose track of the what's-next question-what's the next heading, the next course, and the next altitude? To avoid clearance deviations and conflicts with terrain or obstructions, these questions must be your first priority during instrument flight.

Course intercepts are another task that becomes easy when you reference time. I've heard instructors teach special rules that vary with distance from the station, but if you use time, these rules can be trashed. Don't make instrument flying overly complicated.

A standard-rate turn is normally used to turn on course from the intercept heading. If a 45-degree intercept is used-the common intercept angle when doing your own navigation-a 3-degree-per-second turn will take 15 seconds. If a 30-degree intercept is used-the maximum that air traffic controllers can use when vectoring an aircraft onto a course-the turn will take 10 seconds.

Watch the rate of course needle movement as you approach the desired course. If flying a 45-degree intercept, start the on-course turn when you think the needle is within 15 seconds of centering. If flying a 30-degree intercept, start the turn when the needle is within 10 seconds of centering.

Contrary to popular belief, aircraft have seven flight instruments, the seventh being the aircraft's clock. Use it wisely and you will simplify instrument flying.