On the afternoon of Aug. 4, 2002, a Piper Mirage was in cruise flight above 10,000 feet in the vicinity of Benton Harbor, Mich., when the engine failed. The pilot reported the problem and the controller gave him vectors to the final approach course at Southwest Michigan Regional Airport.
Despite visual meteorological conditions at the time, the pilot followed vectors on a long downwind and he crashed a mile east of runway 27. All three aboard were killed. The question is why.
The NTSB report on the accident is preliminary and does not specify the location of the airplane with relation to the airport at the time of the emergency. But there are 13 airports within 40 miles of Benton Harbor, and the airplanes 30+ mile gliding range assured that a runway was in reach.
This accident is a poster child for the need to understand the factors surrounding glide range and for having the proficiency to maximize range in the event of engine trouble – regardless of whether that trouble comes from catastrophic internal failure, turbocharger troubles or even running out of gas.
Douglas Leet and James Yankaskas, who head the executive committee for the Malibu/Mirage Owners and Pilots Association, analyzed the requirements to dead-stick a landing in a Malibu and, while most other general aviation airplanes dont glide quite as well with the power off as a Malibu, the strategies they developed play in most light aircraft with only a little modification.
Primary among the skills necessary to make a gliding instrument approach successful is a firm understanding of how airspeed, bank angle, aircraft configuration and wind affect the glide range of your aircraft. Armed with that knowledge, you can draw some conclusions about how to fly a gliding instrument approach.
Most single-engine airplanes have best glide speeds similar to the 90 knots Leet and Yankaskas use in their Malibu program. Recall that gliding either faster or slower than your best glide speed – which also varies with aircraft weight – means you are leaving some range on the table.
In the case of the Malibu, a power-off glide at 90 knots gives a descent at about 450 feet per minute. Slow to 80 knots and you drop 550 fpm; speed up to 100 and you lose 600 fpm. At 110 knots, descent is up to 750 fpm. But best glide varies substantially with weight. A Piper Arrow, for example, has a best glide speed of 91 knots at max gross weight of 2650 pounds but only 81 knots at 2100 pounds.
The effect of bank angle is important in two ways. First, banking the airplane increases its descent rate. The greater the bank, the faster the descent. However, increased bank also cuts down the radius of turns and can save altitude by shortening the airplanes track over the ground. Therefore, you must balance your desire to preserve altitude with your need to get to a certain spot. Making a 180-degree turn, for example, costs about 475 feet at a 30-degree bank and about 400 feet at a 45-degree bank, even though the rate of descent is 30 percent higher in the steeper bank.
Actually, 60 degrees works even better, but such steep banks are not something you want to mess around with in instrument conditions unless you are in dire straits and you are well-practiced in the maneuver.
Aircraft Configuration
A windmilling propeller causes substantial drag. There are two ways to reduce the drag – stop the prop or reduce it to high pitch/low rpm. In most airplanes, changing the prop pitch requires oil pressure, so if you plan to change the prop you must do so before the engine loses all power.
Pulling the prop back from low pitch to high pitch can add as much as 25 percent to your glide range. If you leave the prop in flat pitch until it seizes, youll see about 18 percent better glide range.
In an airplane with a fixed pitch prop, stopping the prop will help the glide, but there is a tradeoff. Often stopping the prop means raising the nose to a stall, and that can mean a loss of altitude as you recover. If youre low, you wont gain enough from the prop being stopped to make up for the loss of altitude induced by stopping the thing.
Gear and flaps obviously add drag and should be retracted until the runway is assured. The gear alone can cut glide distance by 40 percent. If the glide is going to be close, consider using the manual extension feature if it puts the gear down more quickly.
In Pipers, for example, the gear is held up with hydraulic pressure. During a normal extension the hydraulic pump also releases the pressure and extends the gear. Extension time: about nine seconds. An emergency extension dumps the hydraulic pressure and uses springs to snap the gear down. Extension time: about two to three seconds. Mooneys and Beech airplanes that require the gear to be cranked down manually take longer, so try to ensure there is enough electricity left to use the electric gear extension when the time comes.
Consider the gear extension to be an irreversible procedure. It may not be, but you cant count on it if the powers off. Extend the gear only when the runway is assured. If you want to add drag and still have the option of removing it, use a slip instead.
The Malibu will glide about 2.7 miles per 1,000 feet altitude at best glide speed. With the gear up and 10 degrees of flaps, the glide slips to about 2.4 miles. Drop the gear along with one notch and the range plummets to 1.4 miles. Two notches plus gear give about 1.1 miles.
While its clear that a tailwind will give you more glide distance than a headwind, it may be surprising how much of a factor this is. Flying with the wind instead of against the wind will increase glide by 50 percent or more. The slower the airplanes glide speed, the more pronounced the effect.
For this reason, punching nearest on the GPS may not result in the most favorable field for your deadstick approach. Consider wind and how well you are already lined up for the approach. An airport thats slightly farther away where youll be pretty much straight in might be a better choice than a nearer airport with one approach on the other side from your position.
Reactions to Power Loss
When the engine dies, remember your ABCs. The first action to take is to set best glide speed. If youre cruising, you may gain substantial altitude during this process. Do not make a zoom climb, however. Loading the wings unnecessarily adds drag and cuts range.
Look below you and consider whether youll make a visual approach to a field or shoot an approach to an airport. Turn in the proper direction. When thats done, you can go through your checklists to try to restart the engine. The one exception to this comes if you know youre playing it close with one of the fuel tanks or there is a prime suspect you can immediately check before turning toward an emergency field.
Airspeed, below, checklists. Pretty easy to remember.
If the ceiling below is better than about 1,500 feet agl and two miles of visibility, head straight to the airport and make a circling descent through the clouds to a deadstick landing. If the weather is low, things get a little more complicated.
The Instrument Approach
Head right for the final approach fix and circle down, if necessary, depending on the distance and the glide characteristics of the airplane. For example, Leet and Yankaskas circle at the FAF (assuming its five miles out) and plan to turn inbound at 3,000 feet agl. Using only airspeed and slips, they plan to arrive at a point two miles from the runway at 1,000 feet agl. At that point the runway is generally assured unless the headwind is strong and they drop the gear and flaps as required.
Leet and Yankaskas have worked out the numbers for their Malibu through flight testing. While the numbers for your airplane will be different – probably more pessimistic due to the Malibus design – the procedures to maximize range are the same.
If you are flying a non-turbocharged single and tend to cruise between 8,000 and 10,000 feet, your glide range may be substantially less. For example, a Cessna 182RG has a glide range of about 13 miles from 8,000 feet. Plan for 3,500 feet at the FAF, which means you can be about eight miles from the FAF and still have a shot at shooting the approach.
A Piper Lance at 8,000 feet at standard temperature has a glide range of about 10 miles. To make it that same five miles from the FAF to the airport requires the airplane to be at least 4,000 feet agl at the fix.
That means if you are cruising at 8,000 feet and are more than five miles from the FAF and the engine conks out, youll not likely make it unless you can cut some corners and still get established on the approach in time.
Once you are established on the approach, use a combination of localizer course guidance, radar vectors and GPS to find the runway. Ignore the glideslope and instead rely on the combination of a stabilized approach and your descent rate calculations to verify whether youll make the field.
Remember to consider both time and distance. Use your descent rate as given by the VSI along with the estimated time of arrival given by the GPS or DME. A 600-fpm descent combined with 1,200 feet agl on the altimeter and your GPS had better give a time of arrival of less than two minutes. Calculate your descent profile in feet per nautical mile and compare that with the distance to the field. Both of these measurements should say youre OK or you should start considering other options.
Also With This Article
Click here to view “Glide Speed and Descent Information.”
Click here to view “Bank Angle Effects.”
