In short. An airport has no single critical load; it has a network of interdependent operations. Power continuity there is a source-to-load architecture in which UPS or batteries carry no-break loads, generators carry essential loads after transfer, and redundancy covers the failure of any one source. Generator capacity should be derived from the approved criticality and interruption tolerance of each function, never from the airport’s total connected load.
Airport power is a resilience architecture
A typical arrangement runs from the utility grid through substations and transformers to MV and LV switchgear and normal distribution. Alongside it sits a generator plant feeding synchronising or emergency switchgear and an essential distribution network. UPS and, where engineered, battery storage carry the loads that cannot tolerate any break. Terminal buildings, IT and communications, security screening, baggage handling, building services and airside systems all draw from this structure in different ways.
Because the functions depend on each other, a failure in one place spreads. Check-in systems are useless if the network switches are down; baggage systems stall if their controls reset. The design question is therefore how the whole chain behaves, not how big the generator is.
Define the facility before the equipment
Airports differ widely. A large international terminal, a regional airport, an airstrip with a small terminal, a cargo complex, a maintenance hangar and an aviation fuel farm each need a different approach. Ancillary buildings on airport land, such as hotels, offices and car parks, usually follow commercial-building practice rather than aviation requirements.
Start with operational criticality
Before anyone asks for a kVA figure, the airport’s authorised electrical, aviation, safety and operational designers should answer a short set of questions for every function.
- Which functions must continue during a grid outage?
- Which need no-break power, and which can tolerate the transfer time of a generator?
- Which can be shed, and in what order?
- Which need redundant sources?
- What is the operational or safety consequence if each function is lost?
Requirements for aviation safety systems, including airfield lighting and navigation aids, are set by the aviation authority and the airport’s approved design. A generator supplier supports those requirements; it must not classify aviation safety-critical loads on its own judgement.
Interruption tolerance decides the technology
Not every critical load has the same tolerance for a break. Matching each load group to the right source is the core of the design.
| Load group | Typical tolerance | Usual supply path | Comment |
|---|---|---|---|
| IT, communications, security and control systems | No break | UPS, backed by generator | UPS autonomy must cover generator start and transfer with margin |
| Airside systems designated by the approved design | As defined by the aviation authority | Dedicated arrangement per approved design | Switchover performance is a regulated requirement |
| Terminal lighting, lifts, escalators, fire systems | Seconds | Generator via automatic transfer | Fire and life-safety loads follow building codes |
| Baggage handling, HVAC, chillers | Minutes | Generator, sequenced after priority loads | Large motors drive the step-load design |
| Retail, car parks, non-essential areas | Can be shed | Normal supply only, or shed on generator | Shedding protects capacity for essential loads |
Connected load is not emergency load
A terminal may have a very large connected demand, but the emergency generation should be derived step by step: connected load, criticality, maximum coincident demand, no-break requirement, motor and transient load, load shedding, restoration sequence, redundancy, autonomy and finally the generation architecture. Each step usually reduces the figure or changes its shape. Our generator sizing guide explains coincident demand and step loads in more detail.
Redundancy and the N+1 check
Airports usually require that the essential load can still be carried with one generator out of service, whether for maintenance or after a fault. That is the N+1 principle.
(N) × Sunit × Lmax ≥ Sess, with N+1 units installed
Here Sunit is the rating of each generator in kVA, Lmax is the maximum loading fraction you accept on each unit, Sess is the essential load in kVA, and N is the number of units that must carry it with one unit unavailable.
Example (illustrative): an essential load of 2,400 kVA with units rated 1,000 kVA and a maximum loading of 0.8 needs N × 800 ≥ 2,400, so N = 3. Four units are installed to give N+1. Paralleled sets also need synchronising switchgear and load-sharing controls, covered on our integrated power systems page.
Restoration sequence and autonomy
When generators pick up after a grid failure, loads should be restored in a planned order: life-safety and designated airside loads, then IT and security, then terminal services, then large mechanical plant. Blocks should be sized so each step stays within the generator’s load acceptance. Autonomy, the hours of operation available from stored fuel, should reflect realistic delivery times in heavy traffic and during monsoon disruption, not ideal conditions.
Testing and maintenance
Continuity is proven only by testing the full chain: UPS, transfer switches, generators, synchronising and load shedding together. Tests should be scheduled with airport operations, documented and repeated after any change. Between tests, preventive maintenance on batteries, starting systems, fuel quality and cooling keeps the plant ready. During upgrades, rental power can provide cover while permanent sets are out of service, and our generator services team handles maintenance on all makes.
Common mistakes
- Sizing generators from total connected load. The plant runs lightly loaded and costs more without improving continuity.
- Assuming UPS autonomy covers any generator delay. A slow or failed start then drops IT and security systems.
- Classifying airside safety loads without the approved design. Regulated switchover requirements may be missed.
- Restoring every load in one block. The step load stalls the plant just when the airport needs it most.
- Testing generators without testing transfer and shedding. Faults in controls stay hidden until a real outage.
What to send us
Send the single-line diagram, the load register with criticality and interruption tolerance for each group, existing generator nameplate photos and the required autonomy. Note any approved design documents that govern airside loads. Use the application engineering enquiry so the review starts from the architecture rather than a kVA number.
Questions engineers ask
Can one large generator serve an airport terminal?
It can carry the load, but it leaves no cover for maintenance or failure. Most airports use several paralleled units arranged as N+1 so the essential load is carried with one unit out of service.
Why do airports need UPS if they have generators?
A generator needs seconds to start and transfer, and IT, communications and security systems cannot tolerate that gap. The UPS carries those loads through the transfer and protects them from the voltage disturbance that follows.
Who decides which airside loads are critical?
The aviation authority’s requirements and the airport’s approved electrical design decide that. The generator supplier provides equipment and performance to meet those requirements. It should not reclassify airside safety systems.
How much fuel autonomy should an airport hold?
It depends on the risk of long grid outages and on realistic fuel delivery times, including traffic and monsoon delays. The figure is set by the airport’s continuity policy. Calculate it from consumption at the expected essential load rather than at full rating.
How should airport generators be tested?
Test the full chain together, including UPS, transfer switches, synchronising and load shedding, on real load where possible. Schedule tests with operations and record the results. Repeat after any change to the system.
Technical content reviewed by Srinivas Reddy, Managing Partner, Reddy Generators. Last updated 19 October 2026.