In aviation ground handling operations, Ground Power Units (GPUs) play a crucial role. They supply the necessary power to aircraft while on the ground, particularly during maintenance or pre-flight preparations. GPUs save fuel, reduce noise pollution, and allow technicians to work on systems that require electrical power. However, like any electrical device, GPUs have their limitations, and overloading them can lead to equipment damage, operational disruptions, and safety hazards. But how can ground support crews and technicians know when a GPU is overloaded? This comprehensive article delves into the causes, symptoms, and diagnostic techniques to identify GPU overloads
Table of Contents
What Is a Ground Power Unit?
Before identifying overload conditions, it’s important to understand what a GPU is and what it does. A Ground Power Unit is an external power supply that provides electrical power to aircraft when engines or Auxiliary Power Units (APUs) are off. Most GPUs supply 28V DC or 115V/400Hz AC power, depending on aircraft requirements.
There are three main types of GPUs:
- Diesel or Gasoline Engine-Driven GPUs (mobile units)
- Solid-State GPUs (stationary, connected to utility power)
- Hybrid GPUs (combination of both types)
Understanding GPU Overload
Overloading occurs when the connected load exceeds the maximum rated capacity of the GPU. For example, if a 90kVA GPU is connected to an aircraft system drawing 110kVA, the GPU is under stress. Prolonged overloading can lead to:
- Overheating
- Circuit damage
- Voltage and frequency fluctuations
- Complete unit failure
Overload is not always obvious. Sometimes it’s silent and slow, creeping up through excessive connected loads over time. That’s why it’s crucial to recognize early signs and use reliable methods to detect overloads.
Signs That a GPU Is Overloaded
1. Frequent Tripping of Circuit Breakers
If the ground power unit built-in protection systems detect an overload, they’ll trip to prevent damage. Frequent tripping, even when loads seem normal, may indicate hidden overloads or imbalances.
2. Unusual Noise or Vibration
Overloaded mechanical GPUs often emit abnormal sounds—rattling, humming, or whining—due to internal stress on generators or engine components.
3. Excessive Heat Generation
Thermal overload is one of the most common signs. If the ground power unit feels excessively hot, even in moderate ambient temperatures, it’s likely overburdened.
4. Fluctuating Voltage or Frequency
Aircraft systems are sensitive to power quality. A ground power unit under stress may output voltage or frequency outside acceptable tolerances, leading to alarms on the aircraft or abnormal system behavior.
5. Delayed or Unstable Start-Up
If the ground power unit takes longer to start or exhibits unsteady behavior during startup, especially under load, it could be a sign that it’s already operating near its limit.
6. Reduced Performance of Connected Equipment
Dimming lights, flickering avionics displays, or malfunctioning testing equipment connected to the GPU may point to voltage drops from an overloaded source.
Tools and Techniques to Detect Overloading
To identify overload accurately, use the following techniques:
1. Ampere Clamp Meter Measurement
Use a clamp meter to measure current on each output line. Compare readings with rated values:
- If a ground power unit rated at 400A is consistently delivering 450A, it’s overloaded.
- Measurements should be done under typical load conditions.
2. Voltage and Frequency Monitoring
Digital multimeters or ground power unit integrated displays often show real-time voltage and frequency. Deviations from standard (e.g., 115V ±3V, 400Hz ±5Hz) indicate stress or improper load management.
3. Thermal Imaging Cameras
Infrared cameras can identify hot spots in GPU components—cables, connectors, transformers—signaling heat stress from overloading.
4. Data Logging Systems
Modern ground power unit often have digital monitoring systems that log load history. Reviewing logs can help detect periods of excessive usage or persistent overloading trends.
5. Manufacturer Diagnostic Software
Some manufacturers offer proprietary software tools that connect via USB or Wi-Fi to display in-depth diagnostic data. These tools can indicate if the unit has been overloaded historically or in real time.
Common Causes of GPU Overload
1. Connecting Multiple Aircraft Systems Simultaneously
Technicians may power multiple onboard systems (lighting, avionics, HVAC) simultaneously, unaware of the total current draw.
2. Undersized GPU for the Aircraft Type
Using a 60kVA GPU for a wide-body aircraft requiring 90kVA is a recipe for overload.
3. Additional Equipment Sharing the GPU
Sometimes ground crews connect external lights, heaters, or tools to the ground power unit output, unintentionally increasing the load.
4. Cable Losses or Faulty Connectors
Poor connections can increase resistance, leading to voltage drops and forcing the ground power unit to work harder to maintain output levels.
Consequences of Prolonged Overloading
1. Component Failure
Overheated cables, capacitors, and transformers may fail, requiring costly repairs or replacements.
2. Reduced Unit Lifespan
Stress and heat accelerate wear, reducing operational life by as much as 50% in extreme cases.
3. Safety Hazards
Overloading can result in electrical fires, smoke, or damage to aircraft systems, posing serious risks.
4. Operational Delays
ground power unit failure during aircraft servicing can delay flights, increase ground time, and impact airline schedules.
Preventive Measures
1. Right-Sizing the GPU
Always use a ground power unit that meets or exceeds the aircraft’s maximum electrical load requirements.
2. Load Assessment Checklist
Before starting the ground power unit, estimate the total expected load. Use a checklist to ensure loads do not exceed ratings.
3. Routine Maintenance
Scheduled inspection of fans, connectors, insulation, and load regulation components reduces chances of overload-related failure.
4. Training for Ground Staff
Educate operators about load limits, overload signs, and proper usage. Well-trained staff can prevent most overload scenarios.
5. Use Load Sharing
If multiple units are available, distribute loads among them instead of stressing a single ground power unit.
Real-Life Example
In 2023, a mid-size international airport in Asia reported a ground power unit failure while servicing a Boeing 787. The cause? A solid-state 90kVA ground power unit was used during winter maintenance when onboard heaters, lighting, and avionics were all active. The actual load peaked at 108kVA, far above rated capacity. Thermal stress damaged internal components, grounding the aircraft for 6 hours. The incident highlighted the need for real-time load monitoring and revised standard operating procedures.
When to Replace or Upgrade the GPU
Sometimes the best prevention is replacement. Consider upgrading the ground power unit if:
- It frequently overheats despite no visible excess load.
- Newer aircraft with higher demands are being serviced.
- Your GPU is over 10 years old with outdated monitoring features.
Modern ground power unit come with load balancing, automatic shutdowns on overload, digital diagnostics, and IoT connectivity—making it easier to avoid overloading scenarios.
Conclusion
ground power unit overloads are a hidden risk in airport ground operations. While not always obvious, their consequences are real—delays, safety hazards, and expensive repairs. Detecting ground power unit overload involves a combination of observation, measurement, and understanding equipment limits. Operators must monitor key signs like breaker trips, heat, and voltage instability, while using the right tools and following preventive protocols.
By choosing the right ground power unit size, maintaining the unit properly, and training staff effectively, you can extend your equipment’s life and ensure safe, efficient aircraft servicing. Stay vigilant, stay informed—and your ground power unit will stay healthy.