Staff Report
Behold the preflight inspection – that superficial perusal of airplanes known by the pilot to be in good condition and maintained to safe standards by crack teams of mechanics.
For many pilots, the inspection is a legitimate tool for making a final decision as to the airworthiness of the airplane. For too many, however, the inspection is a resented intrusion in their desire to light the fire and get into the air. The results include accidents, yes, but they also include expensive mechanical failures that would have been much cheaper if caught earlier.
The problems do not lie primarily with that minority of pilots who conduct the notorious Part 321 preflight (three wheels, two wings, one propeller), but with those who scan the airplane without a good understanding of what it is theyre looking for. Most check the hinges on control surfaces and look at the oil dipstick, but its clear that huge numbers of mechanical problems either are missed by the pilots involved, or else the pilot decides to depart anyway.
We examined more than 26,000 service difficulty reports filed with the FAA as well as nearly 2,000 accident reports and came away convinced that there are a number of areas where pilots are either doing a lousy job inspecting the airplane or else they are choosing to fly with known mechanical deficiencies. Some of the failures represent mere inconveniences, but some are true safety items.
The five areas where we found the most problems were the in the wheels and brakes, retractable gear mechanisms, alternator/battery, fuel supply, and flight controls.
Wheels and Brakes
It seems like the wheels are the ugly side of airplanes. We want them to fly, after all, and airplanes only spend a small amount of time rolling. Small wonder, then, that they are taken for granted.
But look at life from the wheels point of view. They get soaked with cold at altitude, then slammed on the ground to spin up from rest to 80 mph in less than a second, sometimes while scraping sideways or skidding between water and pavement and back again.
The worst tire punishment stems from underinflation, which is fairly typical in an owner-flown airplane. Underinflation causes sidewall flexing and high temperatures that wreak havoc on the tire.
A preflight may include looking at the tires, but the tire can be substantially underinflated before it looks low. A glance around the ramp at a busy general aviation airport shows that few preflights include a tire pressure gauge. While checking the pressure every time might be overkill, once a week certainly is not. This might come as bad news to pilots of fixed-gear airplanes who are forced to remove wheel pants to check pressure.
Preflight should also include a look at the wheel rims to spot cracks. A hard landing or runway pothole can start a crack, which then can propagate until the wheel rim fails and causes the airplane to run off the runway on landing.
The same can be said for frayed brake lines. If the line starts to leak, two things happen. First, brake failure can be imminent. Second, the fluid can cause trouble of its own.
Hydraulic fluid is flammable, and it can cause wheel fires if it gets on the brake assembly and the brakes get too hot. If the fluid coats the brake disk stopping will be severely impaired. If its blown back onto the elevator by the slipstream, it can set up a nasty case of corrosion.
Finally, make sure you check the brakes as soon as you start to taxi from your parking spot every time. Any softness in the pedal is grounds for a more thorough examination, even if they firm up after a pump or two. Even if your intended destination has a 10,000-foot runway and you dont consider braking a concern, there are many events that can conspire against you.
The ground handling of an airplane isnt that great to begin with, so make sure you have all of its assets stacked in your favor before you depart.
Retractable Gear Mechanisms
Closely linked to the question of wheels is the matter of retractable landing gear. A look in the wheel well of your average Mooney, Bonanza or Seneca reveals a maze of links, switches, locks and braces. Some elements are painted steel, some are chrome, virtually all are greasy.
The complexity of the hardware and the need to crawl under the wing to see it leads many preflighters to skip that step. No way around it: Thats a big mistake.
Our studies of FAA incident reports find that half of all episodes that result in a sorry end to a flight involving retractable gear airplanes stem from landing gear failure. Most are not reflected in official accident statistics because the NTSB specifically excludes landing gear failures unless they result in structural damage.
But your wallet doesnt care what the NTSB thinks. A gear-up landing can cost tens of thousands of dollars regardless.
The first step in being able to preflight your landing gear starts when the airplane is in for its annual inspection. Be there when the inspector swings the gear. The airplane is put on jacks and the gear cycled. Watch the locks work and the mechanism in motion.
Ask the inspector to point out spots where welds might crack or where one element may interfere with the others. Ask how the gear door can interfere with the mechanism if its out of rig as well as what those indications might be.
Armed with that understanding of the mechanism involved, your preflight inspections will be more useful because youll have a better idea what to look for and where to look. Resist the urge to clean off all the grease to get a better look, however. Grease is required to keep the gear working smoothly, yes, but it also keeps dirt and corrosion out of the moving parts.
As long as your attention is on the landing gear, review the emergency extension system from the cockpit. Some airplanes, notably Barons, have panels that can be installed so as to interfere with the emergency extension crank. Others, such as some Mooney models, have problematic manual extension systems that are cantankerous and expensive to repair.
The retractable landing gear requires some care. If you fly more than once a month, the annual inspection isnt enough to catch problems while theyre little. You may not have to lie on your back under the airplane before every flight, but you do need to search occasionally for problems before they decide to make themselves known.
Alternator/Battery
A loss of electrical power in flight is sometimes just an inconvenience, but for any airplane used for serious traveling a dead panel can spell trouble, to say nothing about other systems that can be affected by a loss of electrical power, including landing gear, flaps and fuel pumps.
One of the keys to analyzing the electrical system is knowing what the gauges in your airplane actually measure. Some measure demand placed on the alternator, some the system voltage, some the charge/discharge of the battery.
If your battery is weak enough that starting is questionable, give a second thought about taking off after hand-propping the engine or even getting a jump start. With a weak battery, you have little or no reserve electrical power if your alternator fails or the belt breaks.
Checking the health of your battery is easy. When you first enter the cockpit before doing the external inspection, snap on the master switch and see what the voltage is. If the voltage is low, reconsider the trip even if there is enough power to crank the engine. Aging batteries get deposits between the lead plates that can short out individual cells and render them incapable of holding a charge.
But even if the battery and charging system are OK, intermittent problems can arise from something as simple as loose ground wires or corrosion on electrical contacts, such as those that connect a radio to its mounting tray.
Another electrical problem can result from the starter failing to disengage when you release the key or button. A hung starter can be trouble, as it draws a huge amount of current. When the engine catches, make a quick scan of your alternator gauge. If it shows a very high load, shut down immediately and check to make sure the starter is not still engaged to the starter ring gear.
Fuel Supply
There is no aspect of general aviation more frustrating to safety-minded pilots than the tendency of small airplanes to come to grief because they run out of fuel. Ascertaining that there is sufficient fuel aboard is a fundamental responsibility of the pilot, yet dozens of pilots fail the test every year.
Inaccurate fuel gauges can be blamed for part of the problem, but in the end inaccurate fuel gauges are a poor excuse. The problem is exacerbated by the fact that many airplanes need to carry partial fuel to meet the mission requirements their pilots demand. The tendency, then, is to eyeball the fuel level in relation to the indicator tab on the filler neck or to trust the notoriously inaccurate fuel gauges.
Once the pilot estimates the fuel level and reduces that estimate to time in the air, however, it appears that guess turns into gospel, with predictable results. The solution is to dip the tanks with a calibrated dipstick to determine more accurately how much fuel is in the tank. While some airplane fuel tanks cannot be reliably measured with a dipstick, partial fueling can be accurately determined in most models.
But that doesnt mean you can ignore the fuel gauges. Inaccurate or erratic indications can reflect an electrical short in the sending unit or the wiring to it. The result can be a fire in or near the fuel tank.During your preflight inspection, check the level your gauges indicate against the level your dipstick says you have. If they dont agree, find out why. Most pilots have a tendency to ignore the gauge indication because theyre never right anyway, but there may be a hidden danger beyond not knowing how much fuel is aboard.
Once the engine is running, check that the fuel pressure gauge is not fluctuating. A bouncing needle may be a sign the gauge is bad, but it can also foretell a fuel pump failure, failure of a diaphragm in the fuel injection spider, or contamination in the fuel lines or injectors. Takeoff and initial climb is no place to discover the hidden problem wants to come out and play.
Flight Controls
The most troubling aspect of lousy preflight inspections stems from the huge number of control surface failures that show up in service difficulty reports. While many are hidden, some are obvious, including cracks in flap tracks, cracked hinge attach points, frayed trim cables, and frozen pulleys or bellcranks.
These point to simple, superficial inspection during the walkaround in which the pilot passes by items without really looking at them.
While frayed trim cables and frozen pulleys or bellcranks may not be readily apparent visually, their symptoms are. Run the electric trim with your hand on the trim wheel. You can usually feel the component catching as the trim runs through the cycle. Despite this simple test, how many pilots take off without doing any kind of trim test at all?
Some of the most common control surface failures involve the control connections closest to the pilot. The bars that connect the rudder pedals to the cables that transmit the motion back fail fairly often, particularly in training airplanes where a student pilot and instruction battle to overpower each other. To compound the problem, such cracks are not as readily apparent as are, say, cracked yokes – and they are harder to inspect well even if you have the inclination.
Surveys of pilots show that loss of flight controls remains one of the biggest fears pilots have. However, many seem unwilling to put forth more than minimal effort to ensure the flight controls operate properly – and this includes the oft-neglected controls free and proper check found as part of the pre-takeoff checklist of every airplane.
Remember, slop in the system today may show up as an unresponsive control in the future. Just how long it will take for a potential failure to become an actual emergency is anyones guess.
Many preflight inspections make it clear that the pilot intends to fly unless a problem is apparent. While you can usually get away with that, you might want to reconsider your stance periodically and conclude that you wont fly today unless everything is right.
Thorough preflights are time-intensive and get your hands dirty. Human nature being what it is, its not surprising that most preflight inspections dont pass rigorous muster. You can align the odds more in your favor if you periodically give in to the pressure to inspect.
Perhaps not every detail every time, but enough details often enough that youre confident in the condition of the airplane and your odds of flying trouble-free.
Also With This Article
“Some Common Trouble Spots on Retracts.”
“A Word About Engines.”
