Don't let Malfunction Junction become a waypoint on your flight
Mechanical failures are a lot like a hole in one in the game of golf — people know they exist, but few have personally experienced one. Unlike a hole in one, however, when a mechanical malfunction does occur, it's usually preceded by warning signs telling the pilot to beware.
Fortunately, only in-flight structural break-ups nullify a pilot's skills, judgment, and luck — and these are extremely rare. A prepared pilot with a plan can handle other mechanical malfunctions with aplomb, maintaining a high degree of safety.
So how can a pilot prepare to handle common failures?
The facts
According to the AOPA Air Safety Foundation's 2000 Nall Report, the most recent annual study of general aviation accidents, only 15 percent — or 256 — of the accidents studied were the result of mechanical or maintenance causes. Only 8.4 percent — or 27 — of the fatal accidents were caused by mechanical or maintenance factors. Almost half of mechanical or maintenance failures (44 percent, or 114 accidents) were caused by engine and propeller malfunctions. Based on these figures, let's look at some engine problems.
Safety strategies
- Join a type club or other organization devoted to helping owners learn about and maintain their airplanes.
- Attend a type-specific flying proficiency course.
- Study your airplane manufacturer's emergency procedures.
- Attend an airplane systems and procedures course, or commit yourself to learning your aircraft systems, i.e., landing gear, pneumatic, and electrical.
- If you think that something mechanical is amiss, contact your mechanic and explain your concerns in as much detail as you can.
- Do detailed preflight inspections.
- Install an engine monitor — it will help troubleshoot engine problems.
- Install low-vacuum and low-voltage warning lights.
- Keep an airplane trip log with detailed recordkeeping of fuel and oil usage — engine problems are often preceded by changes in fuel and oil consumption.
Common accident scenarios: Mechanical failure
Most mechanically or maintenance-related accidents are not fatal. The accidents studied for this report total 1,701, of which 256 were determined to be caused by mechanical or maintenance failures. The examples listed here are worst-case scenarios:
- Losing control of the airplane while dealing with a landing gear problem.
- Losing control of the airplane after vacuum pump failure while in IMC.
- Loss of communications and navigation capabilities after alterator or generator failure.
- Power failure or power loss at critical stage of flight because of water in the fuel.
- Loss of control or crash short of intended landing field because of fuel exhaustion.
- Loss of control or unsuitable landing area following a propeller blade or blade-tip separation.
- Off-airport landing because of improper management of carburetor ice.
Crankshaft
A broken crankshaft is very rare, but it does happen. On June 14 of this year, aviation writer and pilot Amy Laboda had to ditch her Cessna 210 almost immediately after takeoff from Key West, Florida, when the crankshaft broke. Despite an altitude of only 700 feet, all aboard the airplane survived because Laboda knew her airplane well enough to set up the best-glide speed, open the cabin doors (to facilitate egress in the event of cabin deformation during ditching), and advise her passengers to brace themselves prior to impact.
If your crankshaft breaks in flight, set up best-glide airspeed, squawk 7700, yell for help, find a suitable place to land, and — most important — fly the airplane until touchdown. If oil covers the windshield, sideslips will allow some forward vision. If your airplane is equipped with shoulder harnesses (the best survival tool in any airplane) tighten them before touchdown, and if there is a remote ELT switch, activate it.
Although the chances of a crankshaft failure are very small, the odds do increase if there's been a prop strike. The combined inertia of the reciprocating parts — including the propeller, crankshaft, and the weight of the connecting rods, pistons, gear train, and accessories — is great enough to inflict tremendous damage to an engine during a sudden stoppage. This damage is very seldom visible from the outside of the engine. Whenever a prop strike is serious enough to require sending the propeller to a prop shop for repairs, tear the engine down and send the engine parts to a facility that will certify that the parts are airworthy.
Propeller problems
Should a very small portion of the propeller blade break off or be severely damaged during takeoff or in flight, the pilot may not notice that anything's amiss until his next preflight. But losing an actual piece of a blade, say three or four inches off the tip, will instantly convert the engine and propeller into a severely unbalanced reciprocating mass, resulting in violent vibration. The engine will probably break loose from the engine mounts and thrash around under the cowling until the pilot can puUl the mixture or the primary fuel line breaks, cutting off fuel flow to the engine.
After the vibration stops, turn off the fuel selector and go through the broken crankshaft procedures listed above. With the engine free of the mount, an instantaneous change in pitch center of gravity is likely. Trim as necessary for best-glide speed.
Again, this is a very rare event. What can be done to lessen the chances of prop problems? Keeping propeller blade leading edges smooth and nick-free should be a pilot's primary concern. Pilots should inspect the blades before each flight, looking for leading-edge nicks and other damage. Have a mechanic determine whether any damage is critical before the next takeoff.
Magnetos
If a magneto fails in flight, the engine is not going to self-destruct as long as the pilot reduces power to approximately 60 percent. Power reduction is necessary to keep temperatures under control and reduce the possibility of detonation.
When the compressed fuel-air mixture is ignited by only one magneto, the speed of the resultant flame front is slower, and the combustion pressures are less than those of a normal two-magneto power stroke. Exhaust gas temperatures will go up, as they will on a cylinder with a fouled plug, because the fuel-air charge will still be burning as it enters the exhaust system. Leaning the mixture slightly may help smooth engine operation. Power should be reduced to pretakeoff magneto-check levels before conducting an in-flight mag check, lest the exhaust system be damaged by explosive after-fire. While it's not necessary to switch to the good magneto, doing so may smooth engine operation.
It's safe to continue flying to the nearest airport where maintenance is available, provided you're flying over terrain where the loss of power isn't dangerous.
Fuel system and carburetors
If your engine falters during flight and then returns to normal operation, water or carb ice is usually the culprit. Despite vigilance and rigorous preflight sumping, sometimes a little water is ingested by the engine.
Carb ice can be detected by a loss of rpm when flying an airplane with a fixed-pitch prop, and by a loss of manifold pressure if the propeller is constant-speed. Apply full carburetor heat to clear the ice. While the ice is melting, especially if a lot of it has accumulated, the engine may falter and run rough. Consider leaving the carb heat on until conditions are no longer conductive to the formation of carb ice.
The 2000 Nall Report lists fuel mismanagement as a factor in 66 accidents that resulted in five fatalities. Running out of fuel is the most common fuel-related means of earning a listing in the Nall Report. Should you run out of fuel, trim the airplane for best glide and try to find an airport or suitable landing area.
Pilots should make sure that they know how many fuel sump drains are on their airplane, and where each one is. Sample all fuel system sumps after every refueling. If a sample doesn't look or smell right, make sure that the airplane hasn't been serviced with jet fuel. A simple test is to put a drop or two of the sample on an ordinary piece of paper — a business card works well — and then look at the paper after five minutes. Avgas evaporates with very little trace, while jet fuel leaves an oily residue.
Vacuum system
What should a pilot do to maintain control of the aircraft when a vacuum pump fails, the airplane is in IFR conditions, and the pilot is fearful of losing control of the airplane using partial- panel instruments?
Believe it or not, often the answer is to weave the fingers of both hands together — and put your hands in your lap. Small inputs on the rudder pedals while monitoring the turn and bank/turn coordinator will keep the wings level; level wings eliminate the possibility of a graveyard spiral. This trick prevents abrupt and aggressive pitch changes, which are a primary cause of airframe structural failure, and practically eliminates the possibility of a stall. This technique, combined with trimming for a gradual descent, is also a lifesaver for noninstrument-rated pilots who find themselves trapped above a cloud layer.
Flying IFR with a single vacuum pump is a gamble. The dry pumps used on today's airplanes don't usually wear out; they more often just quit. The first problem with a failed vacuum pump is realizing that the pump has failed. When there's a sudden loss of vacuum, the spinning rotors in the gyro instruments very gradually lose rotational speed before the instruments begin to precess. A pilot hand-flying under instrument conditions may not realize for a few minutes that the vacuum pump has failed. When it dawns on the pilot that the indications from the directional gyro and artificial horizon instruments can no longer be trusted, the pilot without a standby vacuum system installed in his airplane has to immediately switch to partial-panel flying, and recover from what may have become an unusual attitude. The possibility of loss of control during this transition is high.
The best hole card for this gamble is a standby vacuum system or a standby electric artificial horizon (see " Airframe and Powerplant: Standby for Safety," April Pilot).
Landing gear malfunctions
If the retractable landing gear won't extend, don't give up yet. Unless there's some factor that makes it necessary to land immediately, fly around to burn down your fuel load. This may give you enough time to come up with a solution. Try explaining the situation to a unicom operator or flight service specialist. Ask them to call your mechanic or aircraft type club for help. About twice a year, the Cessna Pilots Association technical staff ( www.cessna.org) is called by a tower controller or flight service professional acting as a go-between for a pilot circling nearby with his landing gear in limboland.
If you do end up having to belly in your airplane, be realistic. The idea of trying to stop the prop in a horizontal position, and thereby preventing crankshaft damage to the engine, is dangerous. An airplane has to be flying pretty slow to stop the propeller from rotating, and bumping the propeller with the engine's starter means diverting attention from flying the airplane while low and slow — a situation that is fraught with peril.
The two things you want to do if you're faced with a gear-up landing are to try to pick an inactive runway, especially if your airport is served by commuter or air-carrier traffic, and to belly the airplane in on a paved — not grass — runway. If you set down on the active runway, the chances are pretty good that your airplane will be damaged more during a rushed attempt to move it out of the way than it was in the skid across the pavement. Skidding on pavement is very predictable and does very little actual damage; skidding on a grass runway often digs up rocks and other unseen debris that can tear up major airframe structure, making the repair much more costly and time-consuming.
If your landing gear is hydraulically controlled, make it a practice to check the fluid level regularly. Keep your airplane clean so any leaking fluid will be apparent during your preflight. (You do check the belly of your airplane during every preflight, don't you?)
If the landing-gear reservoir is accessible, carrying a quart of hydraulic fluid and a funnel may be enough to prevent a gear-up landing. Actually, any available fluid can be added to the reservoir in an emergency. Of course, any head-down troubleshooting and repairs are best accomplished while other cabin occupants keep their eyes open for traffic.
Electrical system problems
There are two basic electrical system failure modes: failure of the airplane alternator or generator, or a short circuit resulting in smoke, flame, or a rapid discharge of the battery.
If an alternator or generator fails, a well-charged battery will have enough capacity to power a nav/com radio (or GPS/com) and a transponder for at least an hour. The problem with electrical-source failures is that pilots often fail to notice the failure until the lights dim and the com radios become inarticulate.
The keys to transitioning to a no-source condition are to identify the loss and reduce the electrical system load (load shedding) to preserve the remaining power in the battery. There are various low-voltage indicators on the market for aircraft that don't have one. Aircraft Spruce and Specialty ( www.aircraft-spruce.com) has a nifty stand-alone low-voltage indicator light for about $130. Check with your mechanic to see if he can get a field approval before purchasing this indicator, because it's not STCed.
Any smoke, sparks, or sudden flashes should prompt the pilot to immediately turn off the battery's master switch. If the disturbance stops, the pilot may be able to turn off the problematic circuit with an individual circuit switch (rotating beacon, strobes, or pitot heat, for example). The normal procedure would be to turn off all circuit switches, and then turn the master back on. Then power up the circuits one at a time, pausing between circuits to determine which one causes the problem. If the disturbance returns before you start powering up individual circuits, turn off the master and use your handheld navigation and communication equipment to fly to the nearest airport. If you have an airplane with a retractable landing gear, don't forget to extend the gear before landing.
It's up to you
Most mechanical problems are inconveniences. A proper attitude, the practice of regularly reviewing emergency procedures, a few early warning devices, and a willingness to be vigilant — and humble — will help keep Malfunction Junction from becoming a waypoint on your flight plan.
E-mail the author at [email protected].
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