A basic guide to landing-gear troubleshooting
Landings come in all shapes and sizes. There are those soft squeakers where the first clue to touchdown is the chirp of tires — and then there are the I'm-exhausted slam-it-on mistakes. Same deal for runways. There are billiard-table-smooth ribbons of asphalt without so much as a ripple in the pavement — and then you've got gopher-infested strips that are little more than a squiggly line between potholes. From the best to the worst — yours and the airport's — the landing gear of your airplane must take all in stride.
It does so by being generally quite robust. Certification requirements put a premium on the gear's surviving the most brutal of drop-ins, as well as side loads that even a ripe beginner in a worst-case crosswind landing is hard pressed to reproduce. But the strength of the landing gear is assumed to stem from good overall condition — a subset of proper, timely maintenance.
Although many owners wait until the annual or 100-hour inspection to see whether the wheels are firmly attached to the airframe, this philosophy is the less desirable, often most expensive. Instead, you can and should be evaluating the condition of the gear every time that you fly. And if you discover something untoward, you should fix it immediately; gear problems, as with all other aircraft maladies, do not correct themselves.
The next time you're rumbling down the taxiway, busy looking out for other airplanes and trading the toddler in the back seat a more suitable toy for your newest GPS, notice how well your airplane steers. Is there significant slop in the rudder pedals? Does it take a second or two for the steering to respond to the pedals? (Owners of Grummans, early Bonanzas, and other aircraft without direct nosewheel steering are excused from this line of questioning.) Understand that some aircraft use a spring (or bungee) in the system between the rudder pedals and the nosewheel; there's bound to be some lost movement in the steering. Nevertheless, be looking for an abnormal amount. On high-time Cessnas, for example, you'll often notice very vague steering, as though the nosewheel gets the message only at or near the limit of rudder-pedal travel. Have the steering bungee checked.
Does the airplane track well, or does it tend to pull to one side? First, don't be fooled by rudder trim. On Piper Cherokees, the larger single-engine Cessnas, and some other models, rudder trim applied in one direction will also affect nosewheel steering. Look to see, also, that the rudder pedals are centered at the same time that the airplane is traveling straight down the stripe. There are several linkages in the steering system, and misalignment or poor rigging are always possibilities. Double-check the maintenance manuals, though; some airplanes have a certain amount of asymmetric steering built in to help offset p-factor during the takeoff roll.
Nosewheel steering should be smooth from side to side and have a measure of self-centering force. This varies by design, of course, so it may be helpful to try out another airplane similar to yours to see if they're the same.
Examine the takeoff and landing characteristics during a calm, smooth day. The airplane should lift off with only a moderate amount of additional rudder to counteract the nosewheel's lifting clear of the runway. A sudden swerve or jink could mean that the main gear are out of alignment. It could also signal that the relationship of the nosewheel bias and rudder position are not correct. The service manual will have rigging information. Most aircraft have the nosewheel aligned with the centerline of the airplane with the rudder also centered. Your shop can check the alignment of the main gear by placing a carpenter's level across the face of the wheel rim and measuring the distance between the wheels ahead of and behind the axle centerline. Most aircraft have a modicum of main-gear toe-out — the fronts of the tires angle away from each other — so some difference in the distances is normal. This is part of the alignment that Cessna pilots check first if there is unusual tire wear, particularly on the spring-steel-gear models.
Tire wear is one of the main indicators of gear misalignment. Although each gear configuration will wear its tires differently, you should be looking for changes from the norm. If your mains wear evenly and then suddenly start thinning in only one place, it's time to have your shop investigate further. Also feel for wheel shimmy on your next takeoff or landing. Some aircraft are more prone to shimmy than are others, but it can be destructive to all. First, ensure that the shimmy damper is filled with fluid and securely attached. If your shimmy problem persists, have a local motorcycle shop spin balance the wheel-and-tire combination. Many owners have found that this is the only way to relieve the shimmy burden. Nosewheel shimmy is easily felt through the rudder pedals, but fierce shimmy from one of the mains will make itself known, too. Vigorously apply the brake to one and then the other to help determine if one of the mains is the offending wheel.
During your preflight inspection, make sure that you have proper strut extension all around. This is a critically important but often overlooked item. Common air-oil struts depend upon the air chamber inside to cushion the shock of landings; the remaining oil is essentially incompressible, while air is a wonderful, progressive springing medium. If there's little or no air in the strut, any jolts are transmitted directly to the gear system and thence the airframe.
Owners of retractable-gear airplanes have an additional layer of components to consider. For the most part, retraction mechanisms are remarkably reliable if they're properly maintained. A critical element of this maintenance is the annual gear swing or retraction while the airplane is jacked off the ground. Attend the next one of these, and you'll be amazed at the monkey motion that some gear embrace. It's only when off the ground that you can determine clearances in the major gear components and watch the retraction process for signs of systemic trouble. Be aware of common problem areas, such as hydraulic and electrical glitches in high-wing Cessna gear or deteriorating shock discs in Mooneys or the sequencing of the gear doors on Bonanzas.
Another way to check the gear's condition is to pay attention to retraction and extension times. In electric-gear airplanes (Mooneys, most Beeches, Cessna 310s), slow retract times usually indicate a worn motor or binding in the gearbox that translates the motor's energies into movement of the gear. But don't start at the most expensive part; make sure that the electrical connections are sound before yanking the motor for overhaul. In airplanes that use a hydraulic system — either with an engine-driven pump or a power pack — a retraction system that keeps running for a long time is an indication of problems.It could be a leak, or individual hydraulic cylinders bypassing internally, or a weak power pack; again, go by the service manual and troubleshoot methodically. Some shops apparently choose to overhaul the most expensive component first. A hydraulic system that cycles frequently in cruise flight — many of these systems use the hydraulic up-cycle pressure to hold the wheels in the wells — is also indicative of problems.
Similarly, keep tabs on the electrical performance of the retraction system. Even airplanes depending upon an engine-driven pump have some electrical component to the system. If the switches don't operate as intended, the system may not work properly, and an electrical problem can often masquerade as a hydraulic malady.
At least once a year, you should exercise the emergency gear-extension system in flight. This is not just to give the airplane a workout, but also to keep you familiar with the procedure. Make sure to use the operating handbook's plan and keep the airspeed down to ease extension. Bonanza pilots, for example, are often surprised by how many turns it takes to crank down the gear (about 50) and how much physical effort is required. Far better than the alternative is to determine — on a sunny afternoon when you really don't need the backup — that the hand crank will come off in your hand or the emergency pump is inoperative. While you're up testing the backup system, ensure that the gear-warning devices are working properly. Check your POH. Some airplanes use a throttle-mounted switch to warn that near-idle power and a gear-up indication coexist.
Although it may sound trite, there's considerable truth to the adage that taking care of the gear will help it to take care of the rest of the airplane — and, by extension, you.
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