MRO Management

Why are aircraft batteries so important?

Aircraft batteries

There’s more than meets the eye to aircraft batteries, as Ian Harbison found out when he visited Satair’s new overhaul facility near Heathrow.

If an aircraft main battery fails in flight, the pilot must make a precautionary landing at the nearest airport. If it fails on the ground, the aircraft is going nowhere until it is replaced.

Sounds dramatic for something as simple as a battery, but its primary function, explains Jon Ravenhall, managing director of Satair UK, is to heat the igniters to ensure combustion when the engine is started, hence the importance of having regular overhauls to ensure reliability.

The company, a subsidiary of Airbus, moved into its new facility earlier this year, becoming fully operational in March. This has four times the workshop space, six times the area and 11 times the cubic capacity of the previous facility, which Satair had occupied for almost 30 years.

The move was prompted by a number of factors, he says – the UK Civil Aviation Authority said extra space was needed for growth; the company wanted to expand into electrical component repairs and become a European centre of excellence for dangerous goods; and warehouse space would allow it to become a logistics centre for the Airbus Flight Hour Support programme and support local customers (for example, British Airways stores radomes and leading edges for a fast response for AOGs).

As Satair currently handles around 7,500 NiCad and lithium-ion aircraft batteries a year (a 300 per cent growth in five years), it is one of the world’s largest commercial aircraft battery servicing operations, with some 180 customers, ranging from international scheduled airlines, charter carriers, large low-cost airlines and regional airlines to MRO companies, helicopter owners, business jets and private aircraft owners.

Typically, around 90 aircraft batteries will be in the workshops at any one time. It is also one of the world’s largest aviation battery distributors, representing the top five battery manufacturers – ACME, Concorde, EnerSys-Hawker, MarathonNorco Aerospace and Saft. He says the company is the sole stockist in Europe and holds about 70 per cent of world stock, the rest being in Miami, Singapore and China.

All of the 14 staff made significant contributions to the design, layout and functionality of the new facility, including custom-made cabinets in the workshop, and an additional five new employees have been recruited, with a further four expected by the start of 2019.

The company has started an aircraft batteries technician apprenticeship scheme through the local Way 2 Work initiative, with the first apprentice now engaged. CAA certification is available at age 21.

The lithium-ion batteries special handling unit

The lithium-ion batteries require special handling in the facility. They are stored inside special fire-resistant cabinets that can create a vacuum and send an automatic alarm if a thermal runaway is detected. They are inside a room with a four-hour burn time door. The cabinets also incorporate a valve that allows the fire service to directly inject water.

More general safety features include H2, O2 and CO monitors in the workshop (these gases are generated during the charging process from NiCad and lead-acid batteries) and a high-volume air extraction system. The room is maintained at 19ºC, the optimum temperature for charging.

There is also a complex sprinkler system, with 154 heads throughout the building. The associated tank had to be modified with an increased diameter of 8m so it could meet the 12m maximum height rule near the airport, it holds 457m³ of water.

The environment has not been forgotten in the new building, with extensive use of PIR lighting and 144 solar panels on the roof – the company is paid for excess electricity sold to the grid, but, unfortunately, this cannot be used for battery charging, not least because there are two daily NiCad charging cycles of six hours between 0400 and 1900. Instead, the site developers had to significantly increase the size of the local substation.


Lithium-ion batteries had a bad press because of the fires experienced in 2013 by ANA, Ethiopian Airlines and Japan Airlines on their Boeing 787s. These were caused by thermal runaway.

Satair does not work on this battery, says Ravenhall, which has three components, only on the Saft battery for the Airbus A350, which is fully integrated, combining avionics, charger and battery in a single unit.

This makes maintenance easy – using the Batcare automatic test equipment, the battery is checked and balanced, with any faults being indicated by error codes. A simple check with the Component Maintenance Manual (CMM) reveals whether the fault can be rectified by Satair or that the battery has to be returned to the OEM.


Different NiCad batteries have different overhaul requirements, typically 1,000 flight hours for older Airbus A320 Family aircraft, 2,000 flight hours for Boeing 737s and 2,500 flight hours for 747s.

He notes that life is related to utilisation and batteries are used more on new-generation aircraft as there are more testing and troubleshooting on the ground. A battery may return to Satair several times a year for a 60-minute capacity test, followed by a 12-hour rest.

Aircraft flying above Satair facility at Heathrow

If it passes, it is then charged for six hours, with a check being made on the electrolyte levels in each cell during the final 15 minutes – the charging process can increase the level of liquid in the cell, so this is a way to prevent overfilling.

After a 60 minute cooling period, a general clean and the application of pH-neutral petroleum jelly to the terminals to prevent corrosion, it is ready for dispatch.

If it fails, it is fully discharged, left to rest for 12 hours and then recharged. It can fail up to three times before it is declared beyond economical repair.

A battery can also have five cells fail during its life before it is scrapped, although there is the option of completely replacing all the cells (usually around 20 cells, although some heavy-duty batteries have 40 cells).

He notes that, when a NiCad battery is scrapped, it is almost completely recycled, including steel, copper, nickel, cadmium and the electrolyte. Satair produced 9 tonnes of scrap last year, which was returned to the OEM, making this a closed loop, cradle to grave process.

Once a year, it will undergo a more thorough check. After a 90-minute deep cycle discharge and 12 hours rest, it is stripped, cleaned and tested. Both the vent valve and temperature sensor are also checked.

After rebuild and an insulation check on the case, it is recharged for six hours, cooled for an hour and then subjected to a 60-minute capacity test. This followed by another six charges for hours with an electrolyte level check, a 60 minute cooling period, a general clean and the application of pH-neutral petroleum jelly.

He says it is company policy to exactly follow the procedures in the CMM for each battery type. There are shortcuts, particularly around charging times, but these can produce inconsistent results in use, so the critical need for reliability means no compromises.

One hangover from the 787 incidents is the IATA ban on the transportation of fully charged lithium-ion batteries as cargo, mandating a 30 per cent charge level. Saft batteries are delivered to the company by road at 100 per cent, then discharged to 70 per cent for storage and then 29 per cent for shipment.

Being below 30 per cent means they cannot be certified as airworthy. Inconveniently, this has to be carried out by the customer after recharging. In contrast, NiCad batteries can be held fully charged for 90 days and (subject to the open-circuit voltage) can be released on an EASA Form 1/FAA 8130-3.

This also allows for a rapid response to AOGs.

Satair's aircraft batteries facility


The facility is an Airbus-approved repair agent for Europe, and the OEM is looking to insource more work on electronic proprietary parts. At present, the main workload comes from the electric heater in the galley drain mast for the Airbus A320 Family.

Located on the underside of the aircraft, it is a popular target for ground support vehicles, so there is a constant throughput. However, some 23 other parts have been identified as potential projects, including the A320 Family main landing gear interconnecting strut.

For dangerous goods, which have already seen the installation of containment cages in the warehouse beyond regulatory standards, the company is looking at oxygen generators, escape slide inflation cartridges and fire extinguishers. While not high risk, some items require regular checks.


A large part of the new complex is given over to storage space. Investment has been made in a pallet stacker designed for narrow aisles, and trials have been carried out with a robotic handler that follows personnel – a battery can weigh up to 43kg, so this reduces stress and speeds up the transfer process.

The company is a Known Consignor under the UK Civil Aviation Authority Scheme, which allows it ship material directly from the facility to airside at Heathrow Airport without any further security measures being applied.

This requires that all staff with access to air cargo have received the appropriate aviation security training and that access to the production area is controlled and the production process is supervised. This obviously applies across all Satair UK’s activities and is a useful asset.

Although the building started operations in March, the formal opening ceremony was held in September.

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