TOP-10 GPU Operating Mistakes and How to Avoid Them

Ground Power Units (GPUs) keep aircraft powered safely and efficiently while parked. Yet a large share of faults, delays, and expensive repairs come from avoidable errors: improper grounding, cable abuse, overloading, poor ventilation, ignored alarms, and more. This guide collects the ten most common mistakes and the practical fixes airports, airlines, MROs and military users can implement today.

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🔹Overview
🔹1. No earthing/grounding
🔹2. Skipping power-quality checks
🔹3. Overloading or wrong sizing
🔹4. Wrong start/stop sequence
🔹5. Cable abuse & worn connectors
🔹6. Starving the unit of cooling air
🔹7. Fuel & battery mishandling
🔹8. Ignoring weather/IP limits
🔹9. Ignoring alarms & firmware
🔹10. Undertrained operators
🔹Quick checklist
🔹Let’s talk

Overview

Ground Power Units (GPUs) are the lifeline of modern aviation operations. By delivering stable 400 Hz AC and 28 V DC power, they ensure that aircraft systems remain fully functional during turnaround, maintenance, and pre-flight preparation. When operated correctly, GPUs extend equipment lifespan, minimize downtime, and keep apron operations running smoothly.

However, even experienced crews sometimes fall into recurring bad habits. From improper cable handling to ignoring maintenance schedules, these mistakes don’t just shorten GPU service life — they can also damage sensitive avionics, increase safety risks on the apron, and significantly raise the total cost of ownership.

In this article, we highlight the Top 10 most common GPU operating mistakes observed during audits, service calls, and customer training. More importantly, we share practical, proven tips on how to avoid them — so your operations stay safe, efficient, and cost-effective.

1) Skipping earthing/grounding before connection

A GPU is not just a piece of support equipment — it’s a high-capacity electrical installation. Failing to establish a solid earth/ground connection before use creates a direct risk of electrical shock, arcing, and damage to both the GPU and the aircraft’s sensitive avionics. Beyond equipment reliability, grounding is also a matter of personnel and operational safety on the apron.

Best practice: Always make bonding the first step before any interaction with the GPU or aircraft socket. A simple procedural habit can prevent costly incidents.

2) Skipping power-quality checks (frequency, voltage, phase/polarity)

Aircraft avionics are highly sensitive to power fluctuations. If the GPU’s 400 Hz frequency, voltage, phase balance, or harmonic distortion drift outside of limits — or if the 28 V DC polarity/voltage is incorrect — it can disrupt onboard systems, trigger false faults, or even cause long-term electronic damage. Unfortunately, operators sometimes skip this step under time pressure, assuming “if it powers on, it must be fine.”

Best practice: Always use the GPU’s built-in metering and monitoring functions (or integrated telematics, where available) to confirm parameters are within acceptable limits before energizing the aircraft connection.

3) Overloading the unit or choosing the wrong size

Every GPU is designed with a specific kVA/kW rating. Pushing a unit beyond that rating — whether by connecting an oversized aircraft or underestimating peak loads — puts immediate stress on rectifiers, inverters, and cooling systems. The result: accelerated component wear, unstable output (voltage droop, frequency shifts), and even tripped protection circuits that can disrupt apron operations. Sizing mistakes are just as costly: overlooking start-up surges from cabin air conditioning, long cable runs, or voltage drops often means a GPU that looks sufficient on paper will underperform in reality. For 400 Hz AC units, failing to balance 3-phase loads can add further instability and shorten system lifespan.

Best practice: Always match GPU capacity to real-world load profiles — not just aircraft type. Include startup peaks, cable length, and load balancing in the calculation.

4) Wrong start/stop sequence

A GPU delivers high-current electrical power — and improper sequencing during start-up or shutdown is one of the fastest ways to create voltage spikes, frequency fluctuations, and nuisance trips. Connecting or disconnecting under load doesn’t just interrupt the aircraft’s power supply — it also stresses internal components, shortens the lifespan of contactors, filters, and inverters, and increases the risk of damaging sensitive avionics. Another common mistake is skipping the cool-down cycle. Cutting power abruptly before fans and rectifiers stabilize allows residual heat to accumulate, which accelerates wear and may trigger premature failures in electronic modules.

Best practice:
– Always follow a written Standard Operating Procedure (SOP) for powering on and shutting down.
– Ensure the GPU is energized and stable before connecting to the aircraft.
– Disconnect only after loads are off and cool-down has completed.
– Never rush the sequence — a 30-second delay is far cheaper than avionics repair.

5) Cable abuse and worn connectors

Cables are the frontline of every GPU operation — and unfortunately, also the most abused. When operators run vehicles over cables, bend them below the minimum bend radius, drag them across sharp edges, or store them in “knots,” it creates hidden damage that leads to:
– Overheating and insulation breakdown
– Increased resistance and voltage drop
– Intermittent connections that stress aircraft avionics
– Premature connector wear, creating arcing risks at the plug
– On long cable runs, problems multiply: standard cables can suffer from reactive losses at 400 Hz. Using reactive-compensated aviation-grade cables significantly reduces power loss and keeps voltage within aircraft tolerance.

Best practice:
– Always handle GPU cables with the same care as aircraft fuel hoses.
– Respect the manufacturer’s minimum bend radius and avoid dragging cables across concrete, curbs, or sharp corners.
– Keep cables off vehicle paths and mark safe routing zones where possible.

6) Blocking ventilation or operating with open panels

GPUs generate significant amounts of heat during operation. Without proper airflow, internal temperatures rise quickly, leading to derating, premature wear, and eventual failure of rectifiers, inverters, and cooling fans. Two of the most common mistakes are:
– Blocking air intakes or exhausts — with baggage, cones, or even tarps “to protect from rain.”
– Running the unit with panels open — often done by operators who think it improves cooling, when in fact it disrupts designed airflow and exposes electronics to dust and moisture.
– Clogged filters are another hidden culprit: dust, pollen, and apron debris gradually choke airflow, raising internal temperatures and reducing component lifespan.

Best practice:
– Keep all ventilation zones clear and never cover GPUs during operation.
– Operate with all panels properly closed, as designed airflow paths are part of the cooling system.
– Clean and replace filters on schedule, based on operating hours and local conditions.

7) Fuel and battery mishandling

The power source is the heart of every GPU — whether diesel, hybrid, or battery. Yet fuel and battery care are often overlooked, leading to hidden damage that shows up as unexpected downtime or reduced lifespan.

Diesel & Hybrid Units:
– Contaminated fuel (water, particulates, microbial growth) clogs injectors, reduces combustion efficiency, and leads to hard starts.
– Overdue filter changes accelerate engine wear and shorten injector and pump life.
– Extended idling builds up carbon deposits, reduces lubrication effectiveness, and increases emissions.

Battery & Hybrid Units:
– Deep discharges below the recommended limit accelerate capacity loss and shorten cycle life.
– Storing batteries at 0% state of charge risks permanent cell damage.
– Charging outside the manufacturer’s voltage/current window generates excess heat and reduces long-term performance.

Best practice:
– For diesel: follow OEM fuel filter intervals, drain water separators regularly, and avoid long idling — shut down when not in use.
– For batteries: keep them within the optimal state-of-charge window (typically 20–80%), avoid prolonged deep discharge, and use approved charging systems.
– For hybrids: monitor both subsystems closely; poor practices on either side compromise the whole unit.

8) Ignoring weather limits and IP protection

A GPU may look rugged, but it is still a precision electrical system with defined protection limits. Exposure to weather beyond its IP (Ingress Protection) rating quickly accelerates corrosion, insulation breakdown, and electronic failure.

The most common mistakes include:
– High-pressure washing — forcing water into seals, bearings, and electrical housings.
– Heavy rain or snow ingress — overwhelming drainage paths and reaching control boards.
– Coastal salt exposure — creating conductive paths on circuit boards and corroding connectors.
– Direct UV on rubber seals and cables — leading to premature cracking and insulation loss.
– Ignoring these factors not only shortens unit lifespan but also risks unsafe operation on the apron.

Best practice:
– Always respect the unit’s IP rating for water and dust ingress.
– When not in use, store GPUs under a canopy or indoors to minimize long-term weather exposure.
– In maritime or high-humidity climates, apply anti-corrosion coatings and increase inspection frequency.
– Train operators that “outdoor rated” does not mean “invulnerable.”

9) Ignoring alarms, logs and firmware updates

Modern GPUs are not just power boxes — they are smart electronic systems with diagnostics, protections, and event logging. Yet in the rush of turnarounds, operators often dismiss alarms as “nuisance warnings,” or simply reset the unit without investigating. Over time, this habit masks real issues such as overheating, overloads, frequency instability, or harmonic distortion — until they lead to costly failures.
Another hidden risk: out-of-date firmware. Just like with aircraft avionics, ignoring firmware updates means missing improvements in diagnostics, fault protections, and efficiency algorithms. It also increases the chance of recurring errors, since the root cause is never properly addressed.

Best practice:
– Adopt a strict “No log — no work” rule: no reconnect until alarms are acknowledged and logged.
– Export and review event logs weekly to detect patterns (recurring overloads, temperature spikes, etc.).
– Update firmware on schedule in line with OEM service bulletins to ensure your GPUs have the latest protections and optimizations.

10) Undertrained operators and missing SOPs

The majority of GPU-related apron incidents are not hardware failures — they’re human-factor errors. From cables run over by service vehicles, to skipped grounding, to connectors pulled under load, most mistakes come down to inadequate training and unclear procedures.
Without clear Standard Operating Procedures (SOPs) and regular refresher sessions, even experienced ground crews can fall into shortcuts that cause downtime, equipment damage, or safety hazards. The GPU may be a high-tech system, but it still depends on well-trained hands to operate it correctly.

Best practice:
– Create step-by-step SOPs with visual aids and place them directly on the units.
– Run recurring training every 6–12 months, tailored to local operations.
– Use real-world examples and photos from your own ramp to make lessons stick.

Quick ramp checklist (print & pin)