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Jennifer Roberts

Why Your Air Start Unit Is Broken And How to Fix It

If you are in the aircraft business, you understand your whole business relies on the success of your aircraft. In order to ensure your aircraft are in tip-top shape, you need to ensure the equipment and tools you use are also working efficiently - this includes the auxiliary power unit.

An air start system is one of the main ways to start an aircraft's engines. When this system is used, gas turbine engine compressor spools are turned on and rotate by the action of a very large volume of compressed air. This air acts directly on the compressor blades, driving the engine through a small geared turbine motor. The motors are used to turn on the aircraft's engines. These motors often weigh up to 75 percent less than equivalent electrical systems.

The compressed air needed to perform this action comes from an auxiliary power unit (known as APU), a portable gas generator or from cross-feeding the bleed air from an already running aircraft (if the aircraft is multi-engined). Regular maintenance of air start units makes them reliable workhorses in the aircraft industry. However, if maintenance is done poorly and there are faults in the system, the units may fail. Repairs are costly and time-consuming and will often require the use of expensive air start unit parts.

This type of work can easily be avoided if you know how to take care of the air start units and the auxiliary power units. Both of these tools are incredibly important for efficient ground maintenance work. Let's take a look at some of the most important tips coming from experts in the aircraft industry:


The Basics:

Usually tucked away in a corner of the maintenance area of every airport, the auxiliary power units and the air starters are truly the workhorses of the industry. Without them, the airplanes simply won't be able to take off, bringing all air travel to a halt. They are the basic tools for starting aircraft engines and should be carefully maintained. The APU and the air starters have to be maintained the same ways as you would a powerplant engine. There are thousands of units already at work worldwide, with special variants for each type of aircraft, from large Boeing 747 and 787, to smaller Embraer jets.


Maintenance Tip #1 – Taking care of the connector and the electrical components

The electrical components are the most important aspects involved in an auxiliary power unit. Most air start units have complex electrical systems that are designed with multiple redundancy systems in order to avoid complete failure. However, every sign of intermittent signals or lost signals should be dealt with immediately. Repair these connections as soon as you see even the slightest error or damage. Make sure to use reliable air start unit parts when doing repair work, as it's very important to get everything right the first time. If you postpone repair work, the system may malfunction repeatedly and will show multiple errors. This can lead to further damage and more expensive repair work. For instance, the APU may require a complete overhaul, which could be disastrous, particularly for a small airline.

Fortunately, APU manufacturers have developed simple “connector care” procedures in order to avoid an incident of faulty signals. This is a four-step process that involves the regular cleaning of the connectors in order to improve conductivity. Next, the connectors are torqued with soft-jaw pliers and then taped. This should be done whenever errors occur and during regular maintenance intervals.


Maintenance Tip #2 – Don't postpone replacing parts

Any technical issue, no matter how minor, should be dealt with as soon as possible. Minor errors, like damaged sensors or fuel manifolds, can become serious ones if you don't handle them quickly. Don't wait for someone else to do it. When damage occurs, it should be repaired immediately. Even if the unit still works with a small error or damage, its efficiency can be affected and its fuel flow can be greatly reduced. This will reduce its reliability and will make it prone to future errors and damages.

Always use the best tools and air unit parts when doing maintenance work. Take advantage of shop visits, manufacturer's visits or complete maintenance work that should be done regularly. These are the ideal moments to replace parts that are approaching the end of their cycle. If you do this properly, you can extend the life of the APU and air starters by at least a couple of years. Items that often need replacing are fuel pumps, starters, connector cables, and gaskets. Don't wait for too long before you do this. It will only create more technical problems, which will translate into higher repair costs and more downtimes. Think about your car's battery – you know it’s guaranteed to work for 8 years; however, you don't actually wait till it blows up in order to change it; you replace it before it breaks. The same is for an APU.


Maintenance Tip #3 – Conduct regular inspections and monitoring

Maintenance work should be done continuously in order to make sure the APU and air starters work properly. Make sure you regularly monitor the APU parameters. Also, inspections should be regular and focused on all mechanical and electrical components. Pay attention to any change in parameters or deviations inefficiency. Act promptly whenever you see these changes. Check for common issues, such as oil leaks, faulty electrical signals, and debris. Act quickly in order to avoid more serious technical issues.


Maintenance Tip #4 – Preserve the APU during downtimes

In some cases, the auxiliary power unit will be inactive for weeks or for months. During this period, the APU must be preserved appropriately in order to avoid technical issues. Follow the preservation procedures described in the manual. If you’re unsure, talk with the manufacturer or an engineer. The preservation is required if the APU is inactive for an extended period of time and will guarantee that it will work perfectly when needed again. Also, take care of the exterior of the APU – make sure you cover it with a special PVC sheet (to avoid the accumulation of debris). Similarly, you should apply oil or protective coating to any area that is prone to corrosion.