The sight of an airplane taking-off, with its engines roaring to the maximum, flaps full, and landing gears extended is one every aviation enthusiast lives for. Enthusiast or not, most of us find that our attention stays with an airplane that is landing or about to take-off. These phases of flight, as entertaining as they are for people on the ground, require most concentration from the pilots flying the aircraft. Just like the pilots, the airplane wheels are also hard at work while take-off and landing, bearing the complete weight of the aircraft, its vibrations, and braking loads.
Being the primary contact of an airplane with the ground, imagine the weight and stresses of an entire airplane borne by the airplane’s wheels. You can think of an airplane wheel as an assembly of the central metallic hub and the inflatable tire installed on it. Once a pilot applies brakes, the tires scratch and screech across the runway, making sure that the airplane comes to a halt when demanded. Though it is rare, like all other equipment, airplane wheels may also fail and that would pose a serious question, what if an airplane wheel falls off?
Even though it’s highly unlikely that an airplane wheel would fall off, most times, commercial airplanes are still able to land with one wheel missing. For example, the Boeing B777 has two wheels on the nose landing gear and six wheels on each main landing gear, which means that it may still land normally even if one of the wheels would fall off.
If an airplane wheel falls off, the pilot tries to identify the missing wheel and contacts the Air Traffic Controller (ATC) to get further instructions. The flight manual (FCOM) of the airplane is to be consulted in emergencies as it provides pilots with a stepwise checklist that must be followed.
If an airplane wheel falls off at take-off, the pilot may continue the flight since landing back without a wheel would still be as risky as landing on the destination. At the same time, they would avoid the costly fuel dumping. However, this decision is based on multiple factors such as the airline policy, facilities available at both airports, and the airplane design itself.
In an approach, if the pilot has not crossed the landing-decision threshold and notices the loss of a wheel, a go-around is executed.
But a tire burst or wheel loss after touch-down is difficult to handle, especially for smaller aircraft.
Let us have a look at what happens in small airplanes after the loss of a wheel as compared to a large airplane!
Table of Contents
How do small airplanes deal with a wheel loss compared to larger planes?
Larger aircraft commonly have multiple wheels attached to each landing gear. For example, the Boeing B777 has two wheels on the nose landing gear and six wheels on each main landing gear. Having multiple wheels per landing gear allows some breathing room for the pilot if one wheel is lost.
Small airplanes, on the other hand, do not possess the luxury of having multiple wheels per landing gear, which makes handling a wheel related emergency much more difficult.
Let us take Diamond DA42 as an example; it has one wheel each, on the nose and main landing gear. If it loses one wheel during take-off, the airplane will collapse on the same side, skidding-off the runway into the mud.
Moreover, if a wheel is lost during the approach, a small airplane like the Diamond DA42 may have to perform a belly landing as it would be impossible to land with braking force applied just on one side of the plane.
Owing to this significance of wheels, airlines keep an eye on the maintenance of wheels and their repair intervals. Nonetheless, incidents of wheel detachment still happen and are then investigated by the airlines and regulatory authorities. But have you ever thought what might cause an airplane wheel to fall off?
What may cause an airplane wheel to fall off?
Being certified aircraft components, airplane wheels are designed, manufactured, and maintained under the strict surveillance of regulatory authorities. An airplane wheel is attached to the landing gear with bolts and is aligned and tightened as per specifications noted in the airplane manual.
But during take-off and landing, these wheels experience a lot of vibrations that may cause the tire to misalign or these bolts to loosen, detaching the complete wheel from the landing gear.
Sometimes, a bolt or a bearing may also face material failure and just break-off.
Additionally, simple, and plain human negligence during maintenance or repair can also culminate in an airplane wheel falling off.
Failure, detachment, or tire burst of an airplane wheel can occur, but considering the number of flights performed around the world each day, we can conclude that it does not happen all too often; all thanks to their robust design and material strength!
How strong are the airplane wheels?
While landing, the wheels of a Boeing B777 bear up to 17000kg of weight impacting the ground at above 200km/h and any small failure in wheel assembly can cause its detachment or a tire burst.
The tires of modern large airliners have several layers consisting of vulcanized polymer on the outside with a layer of high-strength threads in the middle and an inner lining of steel. This gives these tires enough resilience to survive several hundred landings before being worn-out.
The wheel hubs of airplanes are generally made up of alloys that can bear the braking stresses applied by the ceramic brakes installed under it. Despite the reliability and sufficient strength of these wheels, it is a widespread practice for airline mechanics and pilots to inspect them routinely.
Does the pilot inspect the wheels (tires) before each flight? (How does a pilot inspect airplane wheels?)
Yes, before each flight, one of the operating pilots performs a preflight check which includes an inspection of aircraft wheels. During the walkaround, the tires are checked for any serious damages such as large cuts, swollen segments, or asymmetrical wear of a tire. If any abnormality is noted, the pilot notifies a licensed aircraft mechanic who inspects the suspected damage in detail.
Airplanes are often given rest periods during the night (or day) known as night stops (or grounding time). These periods are utilized to perform routine maintenance including a detailed inspection of airplane wheels including a check of the tire pressures and brake wear.
With that said, let us have a quick overview of common airplane tire damages!
What are the common damages (wear and tear) on airplane wheels?
Airplanes usually touch the ground at an extraordinary velocity which is instantly translated into the high rotational speed of the tires. As such, once the brakes are applied, you can imagine the stresses borne by these tires within a few seconds.
At this high velocity and brake pressure, a very small object on the runway can cause considerable damage to a tire. Deep cuts are the most common damage to an airplane tire whereas asymmetrical wear of a tire is another one, but it is not reported as often.
An airplane wheel also gets misaligned or skewed if they suffer through a heavy and hard landing, but this is an infrequent scenario. However, in any case, the misalignment of a wheel is easily noticeable for a pilot owing to the high vibration resulting from it.
Furthermore, with each landing, a tire bears a certain degree of wear and tear and therefore requires replacement once the groves on the tire become unnoticeable. The exact tolerance limits of the tire damage including cuts and wear are provided to airline mechanics in the technical manuals of each aircraft.
How frequently are airplane wheels (tires) changed?
Airplane tires are termed as ‘on-condition’ equipment which means that they are replaced once the damages sustained by them exceed the tolerance limits given by the airplane manufacturer.
However, broadly speaking an airplane tire lasts around 200-300 landing cycles or 2-3 calendar months in the case of normal utilization. Furthermore, the airplane brakes have a wear-pin indicator installed on each wheel which tells the remaining life of that brake.
Summary and Conclusion
Airplane wheels bear extreme loads and braking stresses during the take-off and landing phase of a flight and their significance is undeniable. Therefore, when an airplane wheel gets detached during the flight, it becomes a major cause of concern for the operating crew and they are bound to communicate this emergency to the ATC. Although the decision to continue or abort the flight is taken given the airline policies, the pilot has to follow the Flight Manual (AFM/ FCOM) as it details the necessitated steps in view of the aerodynamic and system design of the aircraft.
However, an airplane wheel falling off is not an incident that happens regularly, and considering the number of flights being operated each day, the ratio may just be negligible. The next time you are flying, consider the effort put in by airplane mechanics and pilots to inspect the wheels before each flight and you will feel much safer. Safe flying!
Recommended Course!
