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Five Common Honeywell GTCP36 APU Issues – and How Experienced Technicians Diagnose Them

Five Common Honeywell GTCP36 APU Issues – and How Experienced Technicians Diagnose Them

The Honeywell GTCP36 APU is one of the most proven and reliable systems in aviation, powering a majority of business aviation jets worldwide. When issues arise, symptoms can be misleading. Misdiagnosis is often the cause of repeat removals, extended downtime, and unnecessary maintenance expense.

Based on decades of hands-on GTCP36 APU experience and OEM partnership, StandardAero technicians regularly see the same issues in the field. The following five issues represent common GTCP36 APU troubles encountered in service, as discussed by StandardAero experts Scott VanEssendelft and Craig Cerkez.

1. Generator Drive Seal Oil Leaks

Oil leaks are among the most frequently reported GTCP36 APU issues, but the apparent leak source is not always the true cause. In this video, Scott and Craig explain how to recognize the signs of a generator drive seal leak, and how to determine whether the drive seal is actually responsible for the oil loss.

Why this matters:

Misidentifying the source of an oil leak can result in unnecessary component replacements and repeat removals. Understanding oil migration patterns helps ensure the correct repair is performed the first time, reducing downtime and maintenance expense.

2. Troubleshooting Intermittent Electrical Issues

Intermittent electrical issues are often considered the most challenging GTCP36 APU problems to resolve. Scott and Craig discuss common failure points, effective troubleshooting techniques, and repair missteps that can unintentionally introduce new faults.

Why this matters:

Intermittent electrical issues may not appear during initial inspections, only to resurface in service. A disciplined troubleshooting approach is essential to isolating the root cause and preventing recurring AOG events.

3. Troubleshooting a Compressor Seal Leak

Compressor seal leaks can present in subtle ways, sometimes affecting areas beyond the APU itself. In this segment, Scott and Craig review how to identify compressor seal leaks using visual indicators, odor-related clues, and other operational symptoms.

Why this matters:

Early identification of a compressor seal leak can prevent secondary damage and cabin contamination. Recognizing these indicators allows operators to address the issue proactively rather than reactively.

4. Troubleshooting Generator Gear Splines Erosion

Generator gear spline erosion develops gradually and can lead to more significant mechanical issues if left unaddressed. This video explains how spline erosion occurs, the symptoms it creates, and the repair considerations involved.

Why this matters:

Progressive wear that goes unnoticed can result in unexpected failures and unplanned removals. Understanding when spline erosion becomes a reliability concern supports better maintenance planning and long-term asset management.

5. Troubleshooting an Oil Leak at the Low Oil Pressure Switch

In this demonstration, Scott and Craig examine oil leaks originating from the low oil pressure switch, highlighting a common repair mistake and outlining the correct repair process.

Why this matters:

Improper repairs at the low oil pressure switch often lead to persistent leaks and repeat discrepancies. Applying the correct repair method ensures a lasting fix and avoids unnecessary follow-on maintenance.

Experience That Drives the Best Outcomes

Scott and Craig exemplify the types of StandardAero experts supporting our customers’ GTCP36 APUs, both in the field, and at our service centers.

  • Scott VanEssendelft has 36 years of experience and serves as APU Services Crew Chief at our Augusta Service Center
  • Craig Cerkez has more than 30 years of APU experience and serves as a Senior Field Service Technician with the StandardAero Mobile Service Team

StandardAero has been a Honeywell-Authorized GTCP36 APU service provider since 1993, offering overhaul and heavy maintenance services, as well as global mobile field support.

Need Expert GTCP36 APU Support?

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StandardAero is a leading independent pure-play provider of aerospace engine aftermarket services for fixed- and rotary-wing aircraft, serving the commercial, military and business aviation end markets. StandardAero provides a comprehensive suite of critical, value-added aftermarket solutions, including engine maintenance, repair and overhaul, engine component repair, on-wing and field service support, asset management and engineering solutions. StandardAero is an NYSE listed company under the ticker symbol SARO.