Compressed air for airports and aviation MRO

Where is compressed air used at an airport?

An airport is a group of very different facilities sharing one site: hangars and MRO shops, ground support equipment (GSE) workshops, fire and rescue stations, fuel farms, terminal buildings and cargo sheds. Each one has its own compressed-air needs, and some have strict quality requirements while others need only general shop air. Sorting them clearly is the first step to a reliable and efficient design.

Typical users and values are below. The aircraft maintenance manual, tool maker or equipment owner’s specification always overrides these.

Aircraft systems: what is specialist OEM scope

Aircraft pneumatic systems, oxygen systems, engine starting air, pitot-static testing and similar work are governed by the aircraft manufacturer’s documents and civil aviation regulation. Air for these tasks comes from approved ground carts, test sets and gas supplies under the MRO’s approved procedures. We do not supply or certify equipment for these tasks, and a facility compressor should never be connected to aircraft systems unless the approved maintenance data permits it.

Our role is the facility air system: the compressors, dryers, filters, receivers and piping that serve hangars, workshops and buildings, maintained so that tools and shop processes get clean, dry air at stable pressure.

Tyre inflation: why nitrogen is usually specified

Aircraft tyres are normally inflated with dry nitrogen, as required by aircraft makers and regulators for most commercial aircraft. Nitrogen is inert and dry, which reduces oxidation of the tyre and wheel and lowers the risk linked to overheated tyres. Nitrogen comes from high-pressure cylinders, nitrogen carts, or an on-site nitrogen generator fed by compressed air and followed by a booster.

Where an MRO or airport uses an on-site generator, the compressed air feeding it must be clean and dry, because oil and water shorten the life of membrane or PSA beds. A typical feed-air train is compressor, refrigerated dryer, coalescing filters and often activated carbon, with the generator maker’s inlet requirements as the rule. The booster then raises the nitrogen to cylinder or cart pressure. Ground vehicles and GSE tyres are usually inflated with ordinary filtered shop air.

Hangar and MRO workshop air: typical system design

A hangar air system has to handle large, irregular peaks when many technicians start working at once during a heavy check, and long periods of light demand. A good design is:

1. Two or more screw compressors, often one fixed-speed base unit and one variable-speed unit, so that light loads are handled efficiently and one machine can be serviced without losing air.
2. Refrigerated dryer sized for the hottest ambient and inlet temperature, typically giving about +3 °C pressure dew point.
3. General-purpose and coalescing filters after the dryer, with differential-pressure indicators.
4. Air receiver sized to cover peaks and reduce compressor cycling.
5. Ring main around the hangar with drops to each bay, sloped piping and drain legs so water cannot reach tools.
6. Point-of-use treatment for the paint shop and composite room: extra coalescing and carbon filtration, or a desiccant dryer where the process needs it.

Paint and composite areas deserve their own branch and treatment, because oil and moisture cause coating and bonding defects that are expensive to correct on aircraft parts.

Ground support equipment workshops

GSE workshops maintain tugs, baggage tractors, belt loaders, ground power units, air-conditioning carts and many vehicles. They need air much like a heavy vehicle garage: impact wrenches, grease guns, tyre inflation for vehicle tyres, blow-down guns and parts washers. A piston or small screw compressor with a receiver, a dryer and filters usually suits. Demand is intermittent, so a well-sized receiver matters more than a large compressor.

Terminal buildings and baggage systems

In terminals, compressed air serves building management system (BMS) pneumatic actuators on older dampers and valves, baggage handling diverters and pushers, and maintenance workshops. Many modern BMS installations use electric actuators, but pneumatic control remains common in older terminals and some plant rooms. Control air must be dry and clean; water in small control lines causes corrosion and sticky actuators.

Baggage systems run continuously during operating hours, and an air failure can stop the baggage flow. They justify a standby compressor and a dryer bypass arrangement so that maintenance does not stop the system.

Reliability and standby

For an airport, compressed-air failure rarely stops aircraft directly, but it can delay maintenance releases, stop baggage diverters and slow turnarounds. Good practice is:

• N+1 compressors for hangar and baggage systems, so one machine can be down without losing supply.
• Dryer and filter bypasses with isolation, so treatment can be serviced without shutting down.
• A pre-agreed rental arrangement for a portable compressor and hose connection point if a main unit fails.
• Service planned around the flying programme and heavy checks, not just the calendar.

Energy use

Hangars often run compressors around the clock even when only a few tools are in use at night. Leaks at quick couplings, hose reels and drops add steady waste. Simple measures help: shut off branches to empty bays, repair leaks on a register, set pressure no higher than the tools need (each extra bar costs roughly 7% more power), and use a variable-speed or well-controlled compressor for night loads. Heat recovery from oil-injected screw compressors can supply warm water for washrooms or parts washing.

Indian context

India’s MRO sector is growing alongside its airline fleets, with MRO activity at major airports and dedicated MRO facilities in several states. Hyderabad has an established aviation and aerospace cluster around the airport at Shamshabad, and Andhra Pradesh has several airports with expanding operations. Regional airports under connectivity schemes add smaller hangar and GSE workshops.

The local climate drives design. Summer ambient temperatures of 40–45 °C, and above 45 °C on open aprons, raise compressor discharge and dryer inlet temperatures, so dryers and compressors must be sized for real summer conditions, not 25 °C catalogue ratings. Monsoon humidity raises the water load on dryers. Dust from open aprons and construction blocks intake filters and coolers. Power dips can trip compressors, so restart settings and a standby unit matter.

Common problems and fixes

Worked example: building up the demand of an MRO hangar (illustrative)

A hangar compressor is sized from the tools in use, not from the floor area. The example below is a two-bay narrow-body maintenance hangar with a wheel and tyre shop and one component bench. Tool figures are typical consumptions at about 6.2 bar(g) (89.9 psig) at the tool. The use factor is the fraction of each shift the tool is actually consuming air. Replace the figures with your own tool list.

1. Leakage allowance for a well-maintained ring main at 15%: 102.6 × 0.15 = 15.4 cfm, so 118.0 cfm.
2. Growth allowance (a third bay, more shifts) at 20%: 118.0 × 1.2 = 141.6 cfm, or 141.6 ÷ 35.315 = 4.01 m³/min.
3. Arrangement: either two compressors of about 150 cfm (4.25 m³/min) each, one duty and one standby, or three of about 75 cfm (2.12 m³/min), two duty and one standby. Three smaller machines cost more but match night and weekend loads better and lose only half the duty capacity if one trips. A variable-speed machine as lead suits a hangar whose load swings with the flying programme.
4. Delivery pressure: 6.2 bar(g) at the tool plus about 0.3 bar across dryer and filters and 0.3 bar in the ring main and drops gives a compressor setting near 7 bar(g) (101.5 psig). Setting it higher costs energy, as explained under Energy use above. Locate the compressors, dryers and receivers in a plant room outside the hangar floor, clear of any area the site classifies for fuel vapour, and draw intake air from outside.

Short peaks, such as several sanders starting together, are met by the receiver and are not added to the compressor size. The use factor already averages them out.

Receiver for changeover to standby

If the duty machine trips, the standby needs time to start and load, typically under 30 seconds with star-delta starting. The receiver must hold the hangar above the minimum tool pressure during that time. Usable volume V = demand (m³/min) × time (min) × 1.01325 ÷ allowed pressure drop (bar). For 4.01 m³/min over 0.5 minute with a drop from 7.0 to 6.2 bar(g): V = 4.01 × 0.5 × 1.01325 ÷ 0.8 = 2.54 m³. A 3 m³ receiver, or two smaller ones at the compressor room and the far end of the ring, would be selected. Check the result by timing a real changeover at commissioning.

Nitrogen for aircraft tyres and shock struts: supply and sizing

The aircraft maintenance manual (AMM) and the tyre or landing-gear maker’s data set the gas, its quality, the pressures and the procedure. This section deals only with the ground supply that feeds them. Requirements are often stated as a maximum oxygen content of a few percent by volume and dry gas. Generator purity is normally quoted as 100% minus the residual oxygen, so the setting must meet the AMM limit with a margin. Nitrogen from PSA and membrane generators is inherently very dry, which is one reason it is preferred to compressed air.

Nitrogen is an asphyxiant and gives no warning. Put generators, storage and nitrogen carts in a well-ventilated area, pipe relief valves and analyser vents to the outside, and fit an oxygen-depletion monitor in an enclosed wheel shop, tyre-cage room or nitrogen store. The generator’s waste stream is oxygen-enriched and must also be vented outdoors, away from oil and grease.

Worked example: daily tyre nitrogen (illustrative)

Assume a main-wheel tyre of 0.15 m³ internal volume serviced at 13.8 bar(g) (about 200 psig). Use the actual figures from your AMM.

1. Top-up from 13.0 to 13.8 bar(g): 0.15 × 0.8 ÷ 1.01325 = 0.118 m³ of free gas.
2. Inflation of a newly fitted tyre from 0 to 13.8 bar(g): 0.15 × 13.8 ÷ 1.01325 = 2.04 m³. If the procedure calls for one deflate-and-refill cycle to lower the oxygen, this becomes 4.09 m³.
3. Day with 6 tyre changes and 40 top-ups: 6 × 4.09 + 40 × 0.118 = 24.5 + 4.7 = about 29 m³.
4. A 47-litre cylinder at 150 bar(g) can only be used down to about 20 bar(g), since it must stay above tyre pressure with regulator margin. That gives 0.047 × 130 ÷ 1.01325 = about 6.0 m³ each, so about 5 cylinders a day.

The flow is small (29 m³ over an 8-hour shift is under 4 m³/h). The decision is therefore about logistics and purity control rather than capacity. A small generator works well where cylinder supply is unreliable, provided a booster and storage cover the inflation pressure. Shock struts and accumulators can need nitrogen at pressures well above tyre pressure, so the regulator, hoses and gauges must be rated and calibrated for the AMM pressure. See nitrogen booster compression for the boosting stage.

Point-of-use treatment at each hangar drop

Central treatment sets the base quality. What is fitted at each drop decides whether that quality reaches the user and whether the air is suitable for the tool or process.

Power dips, diesel back-up and restart

The Indian context section above notes that power dips can trip compressors. The table below shows how to make sure the air system recovers on its own.

Test these responses on a planned weekend shutdown rather than discovering them during an aircraft-on-ground event.

How Reddy Compressors helps

Reddy Compressors is an independent multi-brand specialist at Tarnaka, Secunderabad, serving industry since 2002. We sell, rent and service ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and other machines, and we are not an authorised dealer of any brand. We have tie-ups with all major and reputed brands. For airports and MRO facilities we:

• Supply new and used/refurbished screw and piston compressors, dryers, filters and receivers for hangars, workshops and buildings.
• Carry out air audits: leak detection, pressure profiling, dew-point checks and demand logging.
• Provide service, annual maintenance contracts (AMC), breakdown repair and overhaul with over 20 service engineers and technicians covering Telangana and Andhra Pradesh.
• Rent electric or diesel compressors for standby, planned shutdowns and project work, from 50–2,000 cfm and 2–30 bar.
• Identify spare parts from make, model, serial number and nameplate, and confirm fit before quoting, with supply across India.
• Advise on feed-air treatment for nitrogen generators; the generator and booster themselves follow their maker’s specification.

Our track record. We have supplied compressors to leading airport and aviation MRO operators across Telangana, Andhra Pradesh and beyond – new and used machines, long-term rental, and breakdown cover when a facility’s own compressor fails – backed by our own service team.

What to send us

• Facility type: hangar, component shop, GSE workshop, terminal or baggage system.
• Existing compressors and dryers: make, model, serial, running hours and nameplate photos.
• Main users and any specified air quality (paint, composite, nitrogen feed).
• Working pressure needed and operating hours.
• Problems you see: water, pressure drops, high energy use, trips.

Frequently asked questions

Why are aircraft tyres filled with nitrogen instead of air?

Aircraft makers and regulators generally specify dry nitrogen for aircraft tyres because it is inert and contains no moisture. This reduces oxidation of the rubber and wheel, keeps pressure more stable with temperature change, and lowers fire risk from overheated brakes and tyres. Always follow the aircraft maintenance manual. Vehicle and GSE tyres at an airport are normally inflated with ordinary filtered compressed air.

What air quality does an aircraft hangar need?

General hangar tools need filtered air dried by a refrigerated dryer to about +3 °C pressure dew point. Paint, composite and bonding areas need lower oil and particle levels, often with coalescing and activated-carbon filtration, and sometimes a desiccant dryer. The aircraft maintenance data, tool maker and coating supplier set the requirement, and the system should be designed to meet the strictest user on each branch.

Can a workshop compressor be connected to an aircraft?

Only if the approved maintenance data allows it. Aircraft pneumatic, oxygen and engine-start systems need specific approved ground equipment and gases, used under the MRO’s procedures. A facility compressor is designed for tools and shop processes, not for aircraft systems. We supply and maintain facility compressors and do not supply equipment for direct connection to aircraft systems.

Do we need a standby compressor for a hangar?

It is strongly advisable. Heavy checks run to tight schedules, and losing air can stop riveting, drilling and painting across the hangar. Two or more compressors, with dryer bypass and isolation valves, let you service one machine while the other keeps supplying. A pre-agreed rental connection point gives extra cover if a major failure occurs.

How can an MRO reduce compressed-air energy costs?

Start with a leak survey and a repair register, then isolate branches to empty bays at night. Set pressure only as high as the tools need, since each extra bar costs about 7% more power. Use a variable-speed or well-sequenced compressor for light loads and check that dryers are not oversized. An audit with power and flow logging shows where the energy goes.

What compressor feeds an on-site nitrogen generator?

A screw compressor sized for the generator’s feed-air flow, followed by a refrigerated dryer and coalescing filters, often with activated carbon, is typical. The generator maker states the required feed-air pressure, temperature and quality, and those numbers drive the design. Oil or water in the feed air reduces generator life and purity, so treatment maintenance is as important as the compressor itself.

How much compressed air does an aircraft hangar need?

List every air tool and user, multiply each consumption by the number in use and by its use factor, then add about 15% for leakage and an allowance for growth. A two-bay narrow-body hangar with a wheel shop and one test bench might work out at about 140 cfm (4 m³/min). That would be met by two 150 cfm compressors (one duty, one standby) or three of 75 cfm, with a receiver sized to cover the changeover to standby. Your own tool list and shift pattern decide the result.

What purity of nitrogen is used for aircraft tyres?

The aircraft maintenance manual and tyre maker’s data decide. Requirements are commonly written as dry nitrogen with a maximum oxygen content of a few percent by volume. Generator purity is quoted as 100% minus residual oxygen, so a generator for tyre service should be set to meet the manual’s oxygen limit with a margin and fitted with an oxygen analyser and alarm. Some procedures also require deflate-and-refill cycles to bring down the oxygen in a newly fitted tyre.

Can a nitrogen generator fill aircraft tyres directly?

Usually not on its own. A generator delivers nitrogen slightly below its feed air pressure, often around 5–7 bar(g), while aircraft tyres and shock struts are serviced at higher pressures given in the maintenance manual. The usual arrangement is generator, then an oil-free nitrogen booster, then high-pressure storage or a nitrogen cart, and then a regulated inflation station with a calibrated gauge. The nitrogen line should have its own couplings so that it cannot be mixed up with shop air.

What size air receiver does an MRO hangar need?

Size it for the worst event, usually the duty compressor tripping before the standby has loaded. Usable volume equals demand in m³/min times the time in minutes times 1.01325, divided by the allowed pressure drop in bar. For a 4 m³/min hangar, 30 seconds of changeover and a drop from 7.0 to 6.2 bar(g), that comes to about 2.5 m³. Selecting 3 m³ gives a margin. Time a real changeover at commissioning to confirm it.

Related pages

• Industrial applications of compressed air
• Aerospace manufacturing compressed air
• Nitrogen generator feed air
• Refrigerated air dryers
• Rotary screw compressors
• Compressor AMC