ROBERT N. ROSSIER BETTER PILOT / STICK & RUDDER

THE BASICS

Descent Planning Preparing to land

WHILE CRUISE IS ARGUABLY the safest phase of flight, the situation changes as we head toward landing. As our workload slowly increases, our focus begins to narrow, and we can easily overlook details that could lead to a dangerous situation. Statistics reveal that an accident is four times as likely during descent as it is in cruise flight. With proper attention to the details of descent planning, we can more easily manage the demands of the descent and increase the chances of a safe arrival.

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On the surface, it would seem that descent planning is primarily a matter of mathematics. For many light aircraft, we might plan a comfortable 500-foot-per minute descent. Reducing power gradually minimizes the risk of shockcooling the engine; that is, allowing cylinders to cool so fast that they crack. Also, 500 feet per minute is not likely to cause passengers’ ears to pop uncomfortably. And finally, 500 feet per minute makes for easy arithmetic. That’s 1,000 feet down for every two minutes’ flying time. To translate that into miles from the destination, check the groundspeed. At 120 knots, for example, you’re covering two nautical miles (nm) per minute. So you should plan to start your descent four nm out for every 1,000 feet you are above pattern altitude. Example: Let’s say we’re cruising westbound at 6,500 feet mean sea level toward an airport with a pattern altitude of 1,500 feet. Simple subtraction reveals

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we must lose 5,000 feet of altitude in our descent. To do that comfortably, we should start our descent at least 20 miles out. (That’s 4 [nm covered for each 1,000 feet] x 5 [thousand feet we need to lose] = 20 nm.) To make it even easier, most GPS navigators have a “vertical speed to target” option that you can set up in one of the data fields. When that window reaches “500 fpm,” it’s time to consider starting down. Obviously, adjustments may be needed depending on the particular situation.

considerably with altitude, we may wish to alter our basic approach plan to get the smoothest ride possible. The best advice is to begin checking weather well before we start our descent. That includes checking local automated surface observing system (ASOS), automated weather observing system (AWOS),

and automated terminal information service (ATIS) broadcasts or getting the latest weather from flight watch, flight services, or air traffic control. We’ll want to know what the visibility and winds are, and what approach/runway to expect. As part of our procedure, we should also check with other pilots—or just monitor the local

500 FOOT-PER-MINUTE DESCENT

Distance Required Formula Groundspeed (in knots)

Multiplier

60

2

Multiply this

90

3

number by the

120

4

thousands of

160

5

feet you need

210

6

to descend.

As helpful as the simple math problem may be, many competing factors can influence our descent plan. These include weather, traffic, fuel considerations, terrain, and navigation—to name a few. Let’s take a look at these factors as they apply to our planning. CHECK THE WEATHER

Before we even start a descent, it pays to have a good idea of the conditions ahead. In fact, where and how we plan our descent hinges to some degree on the weather conditions both along the route and at the destination airport. Cloud conditions might dictate when and where we initiate our descent to maintain visual flight rules (VFR) conditions. Visibility can also be a key concern. We might do better to remain at a higher altitude if the conditions are hazy below. And let’s not forget about turbulence, especially if we have passengers aboard and want to provide a comfortable flying experience. Since turbulence can vary

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ROBERT N. ROSSIER

A pilot who doesn’t see us approaching on final might decide to taxi onto the runway in front of us at the most inopportune moment.

approach, tower, or common traffic advisory frequency (CTAF)—to find out what folks ahead are experiencing. Again, surface winds are particularly important, as we should have a good idea which runway/approach to expect. For an instrument flight rules (IFR) flight, we might find ourselves continuing past the airport before initiating our approach procedure, and that could affect our descent planning as well. CONSIDER FUEL RESERVES

Maintaining a healthy reserve of fuel is always a good bet, and how we plan our descent can have an impact. If we have a tail wind, it makes sense from a fuel conservation angle to delay our descent and take advantage of the higher groundspeed afforded by the wind conditions aloft. When heading into the wind, we might be better off to descend earlier where the head wind component might be decreased. That’s a consideration that will have to be balanced against other factors such as turbulence, terrain, gliding distance, and so on. CONSIDER NAVIGATION AND TERRAIN

Navigation is another factor to consider in descent planning. Before leaving the more comfortable and low stress environment of cruise flight, be sure to have a good handle on the navigation for the approach phase of the flight. This means reviewing charts and/or approach plates and setting up the navigation radios for the final phases of flight. While it might seem expeditious to navigate directly to our destination airport, terrain considerations should be factored in as well. If our route of flight takes us over water or other forms of inhospitable terrain, we might wish to maintain a higher altitude or alter our course a bit to provide us with more emergency options. Certainly for an approach over water, we should consider planning our approach to remain within gliding distance of shore. CONFIGURE CAREFULLY

How we choose to configure our aircraft during our descent (and approach) can have an impact on efficiency, our

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AB LE AV AI L N O W

workload, and the ease with which we control the aircraft. In terms of efficiency, we do better to make our initial descent in a clean configuration. Dropping the gear and adding flaps will increase our rate of descent, but if we start an earlier descent by reducing power and maintaining a clean configuration, we expend less energy (less fuel) throughout the final phases of the flight. By configuring our aircraft properly, we can minimize the workload for the descent and approach. One way to keep our flying simpler and safer is to minimize the variables, and adopting simple configurations for the descent and approach will help us do exactly that. The initial part of the descent from cruise altitude can often be completed by simply making a minor power reduction. Usually a decrease of 3 inches of manifold pressure, or a 300 rpm power reduction, will get us close to that target 500-foot-per-minute descent rate. As we enter the approach phase, my preference is to choose an airspeed that is close to the best rate of climb speed (VY), and maybe add one notch of flaps. In a retractable-gear aircraft, dropping the gear usually sets up a roughly 300 fpm descent—which will start us down a glide slope without touching the power. If a goaround or missed approach is required, simply adding power will pitch the nose up to the proper attitude for a climb at VY. Once the landing is assured, I extend the rest of the flaps. Any time we’re descending for a landing, it’s a good idea to have our landing light(s) on to improve our visibility to others. Particularly in hazy conditions, turning on the landing light can make the difference between a near miss and a safe situation. A pilot who doesn’t see us approaching on final might decide to taxi onto the runway in front of us at the most inopportune moment.

You are cleared for the approach

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CHECK THE CHECKLISTS

Having and using good checklists can also help reduce the workload and improve safety. The closer we get to the airport, the busier we are likely to be, and the more likely we are to be distracted. From that perspective, it pays to use those checklists earlier in the game rather than later.

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DESCENT CONSIDERATIONS CHECKLIST

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BEFORE DESCENT FROM CRUISE • Check weather conditions (ATIS, ASOS/AWOS, Pireps). • Verify runway/approach. • Check for terrain and obstacles. • Verify groundspeed and plan the descent. • Set radios for arrival. • Complete your cruise descent checklist. WITHIN 10 MILES • Start developing mental traffic picture. • Configure aircraft for approach (flaps, gear, speed). • For IFR approach: verify minimums, timing, and missed approach procedure. • Complete approach/landing checklist. ENTERING PATTERN/AIRPORT TRAFFIC AREA • Verify pre-landing checklist is complete. • Verify wind/runway. • Make necessary radio calls. • Maintain mental traffic picture.

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One technique for remembering the checklist is to always use it before touching the throttle. Before reducing power, get the descent checklist out and complete all the items. While the descent checklist might be simple, some important additions can help keep us out of trouble. A descent or preapproach checklist for IFR flight often includes checking the weather, setting up the radios with the proper frequencies, and setting the altimeter to the local setting for the destination airport. Plenty of accidents occur when pilots forget to complete their pre-landing checklist. Distractions abound during the approach phase of the flight, including radio calls and traffic avoidance. I’m a firm believer in the “three strikes” approach to pre-landing checklists, which means I give myself three chances to get it right. The first shot at the pre-landing checklist comes before entering the airport traffic pattern. This is an opportunity to make certain anything that can or should be done gets done. I like to review the checklist again once in the pattern (preferably on downwind) to make certain all items have been completed. Just in case there were any distractions earlier that could have fouled up my checklist, I use a GUMP (gas, undercarriage, mixture, prop)

or MPG (mixture, prop, green light) check on final—just to make certain I don’t end up on the evening news. USE FLIGHT FOLLOWING

No discussion of descent planning is complete without mentioning the importance of resource management, and one of the best resources for a VFR approach is radar service in the form of flight following. Even at busy terminal areas, most controllers would rather communicate with an aircraft than guess what it’s doing and try to keep IFR traffic away from it. In addition to assistance in identifying traffic, air traffic control can provide us directly or indirectly with valuable information. By listening to what’s happening with aircraft ahead, we’ll have a better idea of what to expect. Descent planning isn’t exactly rocket science, but there are plenty of considerations that can make our descents and approaches easier and safer. By planning our descents carefully and thoroughly, we improve the chances for an uneventful arrival at our destination. Robert N. Rossier, EAA 472091, has been flying for more than 30 years and has worked as a flight instructor, commercial pilot, chief pilot, and FAA flight check airman.

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