This article explores consumable aircraft parts. Specifically, looking at what factors play into the need to replace these parts on a regular basis, performance challenges and safety precautions.
Rather than look just at the actual parts I think its important to mention the Pilot. How the pilot manages the planes decent on landing, for example, can have a big impact on the wear and tear placed on these parts. Upon touchdown, the aircraft’s weight, combined with the vertical speed, creates a significant impact on the wheels and brakes.
The average vertical speed in a normal landing is around 2 meters per second (6.6 ft/s), which translates to approximately 400 feet per minute (fpm). Pilots aim for a lower vertical speed at touchdown for a smoother landing. Ideally, this would be less than 200 fpm. Anything over 400 FPS is considered a hard landing and can put excessive stress on the landing gear. wheels and brakes.
Aircraft brakes can get extremely hot during landing, especially on larger aircraft or when performing a rejected (aborted) takeoff. When the brakes are applied, friction between the brake pads and discs causes this energy conversion, resulting in a significant temperature increase.
Here’s a breakdown of the temperatures they can reach:
Normal Landing – During a typical landing, aircraft brakes can reach temperatures between 300°C (572°F) and 500°C (932°F).
Hot Landing – In situations like a rejected takeoff or a heavy landing, brake temperatures can exceed 500°C (932°F) and potentially reach up to 1000°C (1832°F) or even higher in extreme cases.
With these hot landings, overheating can reduce the effectiveness of the brakes or even lead to complete failure. In extreme cases, overheated brakes can ignite nearby flammable materials, such as tires or hydraulic fluid.
Regular maintenance and inspections are crucial to ensure the brakes are in good condition. Brakes like many other critical components are monitored by the FAA who provide advisory circulars for inspections, maintenance and replacement. Manufactures often release service bulletins to address specific issues.
Brakes like tires have wear limits on the brake pads and discs showing clearly when they need replacing. Aircraft manufacturers provide detailed maintenance instructions for their aircraft, including specific information on brake inspections and replacements.
Ever wondered why the planes tires smoke on landing? It’s not due to a poor landing or failed equipment. The smoke is due to the tires briefly skidding as they spin to catch up with the aircrafts speed. When the tires first touchdown, they are not rotating at the same speed as the aircraft. To give you an idea commercial Jets land at between 130-160 mph.
Factors that play into the frequency of replacing tires include aircraft weight, landing frequencies and operating conditions. Regular inspections of tire pressure, maintenance checks (cuts, wear and punctures for example) and identifying tire age help assess whether replacements need to be made.
Most tire brands have “wear” indicators to help identify worn tires. Yet even with minimal wear tires should be replaced after a certain period due to degradation, typically, around 6 years. Always check with the OEM e.g. Goodyear for guidelines on maintenance, inspections and safety.
Aircraft windows are incredibly durable. Windshields on business jets are typically around 1.5 inches (38 mm) thick. Aircraft that fly at higher altitudes require thicker windows due to increased cabin pressurization. This substantial thickness is also necessary to withstand bird strikes and hailstones. However, windows can still develop problems over time. Here’s a breakdown of the common reasons why windows often need replacing:
Crazing is the formation of a network of fine, hairline cracks on the surface of the window. It’s a common issue, especially on the outermost pane of the window. Crazing is more aesthetic and does not necessarily impact the integrity of the window, that being said maintenance professionals have to inspect the windows regularly to ensure deeper cracks do not appear.
Causes of crazing:
Stress from pressurization: The constant cycle of cabin pressurization and depressurization puts stress on the windows, leading to tiny surface fractures.
Environmental factors: Exposure to UV radiation, extreme temperature fluctuations, and high-altitude conditions can accelerate the aging process of the window material, making it more prone to crazing.
Chemical exposure: Cleaning with harsh chemicals or accidental exposure to substances like ammonia can damage the window surface.
Bird strikes: Collisions with birds, especially during takeoff or landing, can cause cracks or even shatter the window.
Foreign object debris: Small objects on the runway or in the air can strike the window and cause damage.
Hail: Hailstorms can cause significant damage to aircraft windows, especially at high altitudes.
Othe factors include, ageing, manufacturer defects and improper maintenance.
Aircraft batteries provide power to critical systems like navigation, communication, lighting, and engine starting (APU). A battery failure can have serious consequences.
Capacity Loss: Batteries gradually lose their ability to hold a charge over time. This can lead to reduced performance and an inability to power systems for as long as needed.
Internal Resistance: The internal resistance of a battery increases with age, reducing its ability to deliver current effectively.
Sulfation: This chemical process occurs in lead-acid batteries, reducing their capacity and lifespan.
Voltage Drop: A battery’s voltage can drop below the required level, affecting the performance of electrical systems.
Loose Connections: Loose battery terminals or wiring can cause intermittent power loss or complete failure.
Corrosion: Corrosion on battery terminals can hinder electrical flow and reduce battery performance.
Thermal Runaway: In some types of batteries (like lithium-ion), a thermal runaway can occur, leading to overheating, fire, or even explosion.
There are several safety measures that must be taken to optimize battery life and replace batteries when necessary.
Regular Inspections: Aircraft batteries are regularly inspected and tested to identify potential issues early on.
Preventive Maintenance: Batteries are replaced according to manufacturer recommendations and maintenance schedules to minimize the risk of failure.
Redundancy: Many aircraft have backup batteries or emergency power systems to ensure critical systems can still function in case of a primary battery failure.
Its clear that these aircraft parts have to perform at a very high level, and are under immense pressure. The pilot has to fly well and safely, especially during take off and landing impacting how often parts need replacing. Also, extreme temperature changes and cabin pressure are other factors that place parts under duress and therefore lead to regular replacement.
Other factors are the nature of the parts themselves; batteries naturally degrade over time as do tires even with minimal use in both cases. These replacement parts are incredibly well designed to handle the challenges as highlighted. This makes it easy to understand why many of these parts are so expensive. Having spares on hand is critical because as highlighted there are many factors outside of your control as a pilot, owner or mechanic that can create the need for emergency repairs.
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