In today’s competitive aviation marketplace, airlines are constantly seeking ways to boost revenue and minimize fleet downtime. A single maintenance issue, if severe enough, has the potential to delay or ground a flight, which can wreak havoc on departure schedules, possibly require a replacement aircraft, create a financial burden for the airline and frustrate passengers eager to get to their destinations. The integrated drive generator (IDG) is an especially critical component. Aircraft generator failure is one of the most important maintenance challenges airlines face today. Unplanned generator maintenance and removals are incredibly costly.

Here we will briefly review how an IDG works, the maintenance issues commonly associated with them, and how Avborne Component Solutions – an AerSale® company – will keep yours in the air instead of on the ground.

The IDG: What it is and what it does

In short, the integrated drive generator is an alternating current (AC) generator installed on a turbine engine. An IDG incorporates a brushless, three-phase AC generator and a constant speed drive in a single component. It is the main source of AC electrical power on an aircraft driven by the engine through the accessory gearbox. To provide the constant 400 Hz frequency AC electrical power needed by aircraft electrical systems, it must convert variable engine input speed to a constant output speed for the generator.

Consider that on a Boeing 737 Next Gen there are two IDGs providing redundant capability, one per CFM-56 engine, and engine RPMs vary considerably from taxi, takeoff, cruise, and descent. 

Due to the extreme internal forces and temperatures IDGs experience, they are incredibly robust components and usually have a short-time overload capability of approximately 185 percent of the rated power. For example, the 120-kilovolt amp IDG of the Boeing 777 can safely deliver up to 226.8kVA for five minutes every 1000 hours of operation.

Troubleshooting of IDGs is simplified since it is a line-replaceable electrical generation component on the engine, meaning it can be swapped out relatively easily when problems occur. However, determining the cause of a malfunction requires in-depth testing and the use of sophisticated test stand equipment. This is where Avborne Component Solutions excels and is a recognized industry leader.

Common problems with IDGs

Eventually, any airplane component under torsional stress and high heat – no matter how hardened – will experience some type of failure. These are just a few of the more common issues found in IDGs.

• Internal and external leakage from seals and gaskets – Some high thermal stability oils can be aggressive on elastomer seals, causing swelling, brittleness, and cracking, leading to premature generator removal. Due to high operating temperatures and constant expansion and contraction of components, seal and gasket replacement is a problem more typically found in high time, high cycle IDG’s.

• Diode failure – A diode is a semiconductor device allowing electricity to flow in one direction. It can fail if turbine oil does not have adequate electrical conductivity. For example, on the Airbus A340, if the IDG is engaged when the oil is extremely cold (-22 to -40 degrees Fahrenheit), a more viscous oil can physically damage the diode pack. There must be adequate electrical conductivity to dissipate through the lubricant. If the ambient humidity is too low and the lubricant lacks sufficient conductivity, a powerful electrical discharge may result that causes permanent damage to diodes in the generator control circuitry.

• Corrosion and plugged filters – Oil oxidation and bits of metal from worn IDG internal components can lead to filter plugging and differential pressure indication alarms on the flight deck. At some point, development of sludge, corrosion damage, and blocked filters will force IDG maintenance or overhaul.

• Electrical frequency variation -Whether it is the IDG itself, or the generator control unit (GCU), if a significant enough electrical frequency deviation occurs – either too high or too low – this will impact other electrical systems on the airplane since power is not remaining at a consistent 400 Hz. This also indicates the pilot needs to disengage the IDG to prevent secondary damage.

• High temperatures – High temperature issues are typically found if the unit is moving towards a catastrophic failure. Either the pilot manually disengages the IDG, or the system thermal failsafe will automatically disconnect it from the engine. Once the IDG is disengaged, it cannot be reengaged in the air and must be reset on the ground.

Other common issues include hydraulic pump pressure charge drops, permanent magnet generator charge drops, insulation issues, bearing failures, and unbalanced dynamic components such as rotors and exciters.

Secondary damage in the IDG occurs when the unit fails for one reason but kept engaged on the engine. As a result, increasing temperatures then cause secondary damage to other components. A timely disconnect of the IDG by a pilot before thermal failure can prevent secondary damage and significantly reduce repair costs.

How Avborne handles IDGs

With so many types of issues that can occur with IDGs, you need an MRO partner who is thoroughly versed in their repair and overhaul. Avborne Component Solutions has over 40 years of combined experience repairing IDGs and CSDs. Avborne strictly adheres to all quality standards, rigorously document all procedures, and employs a highly trained, certified, and qualified workforce. Avborne’s record speaks for itself, with IDGs repaired at their maintenance facility in Miami, Florida, proven to remain on wing longer than repairs from OEMs or other competitors. Additionally, Avborne’s on-site engineering team has developed and manufactured all IDG and CSD tooling, and its integrated rewind shop enables Avborne to control repair lead time. This results in significant cost savings for customers.

Every IDG has its own test procedure that involves running it at different power states, from idle to takeoff and cruise. Avborne follows those test procedures and documents the results, and provides them to the customer. When an IDG arrives at Avborne, it undergoes five initial visual inspections to determine the extent of any necessary repairs. Technicians look for the following:

• Peeling paint – The unit could be overheating.
• Input rotation – Is the IDG turning, locked up, or making noise?
• Leak check – Avborne is one of the few MROs that completely submerges the entire unit in a cleaning solvent to find difficult leaks. Small leaks found at room temperature become big leaks at operating temperatures.
• Inlet and outlet filter checks – An industry standard check to look for metal shavings and other foreign object debris (FOD).
• Metal chip detector – Some IDGs use a magnetic chip detector to find metal shavings in the oil.

Since the failure of either the IDG or GCU is potentially the source of the problem, Avborne thoroughly inspects and services them both. After a repair or overhaul at Avborne, IDGs perform like new and often have many components reset to zero time. Lastly, if an airline can thoroughly describe the IDG problem encountered, including error messages from the flight deck, Avborne can focus on a specific repair versus performing a complete overhaul allowing for a faster turnaround time and reduced overall costs.

Preventing IDG problems

There are two IDG problems that are easily avoidable, and both revolve around oil. The first is ensuring the IDG oil is at the proper level. This is done as part of basic ground maintenance, but there is a catch. When an airline receives a unit back from Avborne, there is no oil in it. Airline ground personnel may fill the reservoir until it reaches the full mark, but they often do not compensate for the oil lines being empty. This results in a low oil state for the IDG and potentially causes all the attendant problems that accompany too little oil circulating through the unit. The solution for this is to run the engine for approximately one minute, shut it down, then add more oil to the IDG.

The second issue is not mixing different types of oil. Since oils have different viscosities and breakdown at different temperatures, mixing oils can result in hot spots inside the IDG due to uneven lubrication and cooling. It can also increase the accumulation of sludge in the filters. While the type of oil used in IDGs is based on operator preference, Avborne recommends using Exxon 2380 oil.

IDG advantages with Avborne

Avborne’s highly experienced, in-house engineering development team operates under an FAA Open Class Rating. It is continuously introducing innovative cost-saving repair and overhaul regimes by using the latest in testing technology and a very sophisticated, state-of-the-art IDG test stand.

Results are our reputation at Avborne. Strict adherence to quality standards has earned wide recognition from the aviation industry’s governing bodies, including the FAA, EASA, and CAAC accreditations. Avborne customers always receive the highest quality parts, unsurpassed service and attention, and unparalleled certification and trace documentation for every asset transaction.

Avborne Component Solutions, an AerSale® company, is a certified Federal Aviation Administration (FAA) 145 repair station in Miami, Florida, and a recognized leader in providing highly technical and specialized repair services covering a broad range of commercial and military aircraft systems, including hydraulic, pneumatic, electronic, and landing gear components. It is one of the few component MROs operating today under the authority of an FAA Open Class Rating. This licensing allows Avborne to initiate its own FAA repair validation packages for expedited introduction of new repair and overhaul capabilities well in advance of traditional MRO participants.

A global aviation leader, AerSale specializes in the sale, lease, and exchange of used aircraft, engines, and components, in addition to providing a broad range of integrated maintenance, repair, and overhaul (MRO) services and engineering services for commercial aircraft and components. AerSale also offers asset management services to owners of end-of-life aircraft and engine portfolios. Headquartered in Coral Gables, Florida, AerSale maintains offices and operations in the United States, Europe, and Asia. For more information about how AerSale can be your one-stop source for non-stop service, visit www.aersale.com.