Fixed 400 Hz + PCA or mobile GPUs — how should an airport phase stand electrification?

When an aircraft is on stand, it needs electrical power and conditioned air. It can get them three ways: run its own Auxiliary Power Unit (APU) — the dirtiest and most expensive option — take power from a mobile diesel GPU and a mobile air unit, or plug into fixed 400 Hz ground power and Pre-Conditioned Air (PCA) built into the stand. The strategic decision for an airport is not "which is best in theory" — fixed is — but how to phase the move to fixed infrastructure across a real apron with mixed stand types and a capital budget. This brief is about that retrofit-sequencing decision, not the basics of how 400 Hz power works.

The three sources, ranked

Source	Emissions on stand	Cost per turn	Infrastructure	Best role
APU (aircraft's own)	Highest (jet fuel burn)	Highest	None	Last resort; eliminate where possible
Mobile diesel GPU + air	High (diesel) but less than APU	Medium; fuel + labour	Minimal	Remote/transitional stands; bridge step
Fixed 400 Hz + PCA	Zero at stand (grid power)	Lowest per turn	High capital	Permanent gated/contact stands

The whole point of stand electrification is to push aircraft down this table — off the APU first, then off diesel — so the apron is quieter, cleaner and cheaper to operate.

Why fixed wins long-term — and why you cannot do it everywhere at once

Fixed 400 Hz and PCA, drawn from the grid, have the lowest running cost per turnaround and zero local emissions at the stand. But they require real capital and civil works: cabling, pits or pop-up units, PCA plant and the electrical backbone to feed them. Two technical points shape the retrofit:

PCA is a big electrical load. A PCA unit's compressors can briefly draw nearly as much power as the aircraft itself, so the stand's electrical design must account for whether GPU and PCA share a circuit or run on separate feeds. Underestimating this is a common retrofit error.
Sizing must reflect worst-case heat. In Gulf conditions the PCA load is driven by cooling a hot cabin, so capacity has to be sized for summer worst-case, not average — under-sized PCA simply cannot pull an A380 cabin down to temperature on a 45 °C afternoon.

You therefore cannot electrify a whole apron in one step. The realistic path is to prioritise the stands that pay back fastest and bridge the rest with mobile GPUs.

The phasing decision — a practical sequence

1. Target high-utilisation contact stands first. A busy gated stand sees many turns a day; eliminating APU and diesel there delivers the largest emissions and fuel saving per unit of capital. These are the first candidates for fixed 400 Hz + PCA.

2. Use mobile GPUs as the bridge on remote and transitional stands. Where fixed infrastructure is not yet installed, or stands are used intermittently, a mobile GPU still gets the aircraft off its APU — a real near-term emissions and noise gain — without the capital of fixed works. Mobile units support a phased rollout and strengthen operational continuity while the civil programme runs.

3. Choose hybrid mobile units to cut the bridge's own emissions. A pure diesel GPU is itself a pollutant. Hybrid GPUs that switch intelligently between engine and battery (ElectroAir's APA-65 / EACR-45 class is one example) cut fuel, noise and emissions versus straight diesel, and battery eGPUs (such as the ITW GSE 7400, where replacing one diesel GPU is cited as avoiding around 50,000 kg of CO₂ a year) go further where charging is available. The bridge step does not have to be dirty.

4. Build electrical capacity ahead of the fixed rollout. Because PCA loads are heavy, the grid and substation capacity often needs upgrading before fixed points can be added at scale. Sequence the electrical backbone so it does not become the bottleneck that strands installed pits.

5. Match the kit to the aircraft mix. Size fixed and mobile power to your largest regular type (A380/Code-F stands need more than narrowbody stands). GPU capacity is commonly specified in the 90–180 kVA range for larger aircraft; pick the rating from your worst-case stand demand, not the average.

GCC relevance

The Gulf case for electrification is unusually strong on two counts. First, fuel and emissions: APUs and diesel GPUs burn fuel on an already-hot apron, and getting aircraft onto fixed grid power removes both the local pollution and a meaningful fuel cost. Second, heat-driven PCA demand: cooling a soaked cabin in Dubai, Doha or Riyadh summer is a large, sustained load, which both raises the value of efficient fixed PCA and forces careful electrical sizing. The hubs running large A380/widebody fleets have the high-utilisation contact stands where fixed 400 Hz + PCA pays back fastest — and the remote-stand growth where hybrid mobile GPUs bridge the gap.

Honest limitations

Fixed infrastructure is capital-intensive and disruptive to install on a live apron, and its payback depends on stand utilisation — a fixed point on a rarely-used stand may never justify its cost, which is exactly why mobile GPUs remain the right answer there. Mobile units, even hybrids, do not match the zero-stand-emissions of grid-fed fixed power; they are a bridge, not a destination. And PCA sizing in extreme heat is genuinely hard — validate capacity against summer worst-case, not vendor nominal ratings.

The bottom line

Electrify in priority order: kill the APU everywhere first, then convert high-utilisation contact stands to fixed 400 Hz + PCA where the turn volume justifies the capital, and bridge remote and transitional stands with hybrid or battery mobile GPUs in the meantime. Size everything — especially PCA — for Gulf summer worst-case, and build the electrical backbone ahead of the fixed points so it does not become the constraint.