Commercial passenger aircraft are struck by lightning on average once a year. Although the effects on aircraft and helicopters of low-amplitude lightning strikes are minimal, high-amplitude strikes can result in expensive delays and important repair and maintenance. An EU-funded project has developed a prototype in-flight system to measure the properties of actual lightning strikes and their possible effects on aircraft.
Actual data from lightning strikes have been gathered on test aircraft in the past and have provided adequate input on the effects of in-flight lightning strikes for years. However, not a lot of in-flight lightning strike data exists. More data means more knowledge of the phenomenon, enabling aircraft designers to optimise the structure and reductions in maintenance costs after a strike. Real-time strike detection and transmission of information to maintenance crews means that preparations for inspection or repair can be made before the aircraft has landed.
The 'In-flight lightning strike damage assessment system' (ILDAS) project, a joint effort of 12 European companies, developed and validated a prototype system which assesses the effects of a lightning strike directly on the aircraft and provides data which could be used to improve future aircraft design.
The project developed a system which uses advanced, smart sensors on the fuselage and wings of an aircraft that characterise lightning-strike parameters and current flowing through the aircraft skin during an in-flight strike. Perhaps more importantly, the project partners created cabin-interior sensor solutions which provide a much better starting point for developing an on-board ILDAS system for modern commercial airliners, because they are considerably easier to install in the aircraft.
"We developed a measurement system capable of measuring actual lightning strike data," says Rob Zwemmer, ILDAS project coordinator at the National Aerospace Laboratory in Amsterdam. "In addition, a very promising window sensor has been successfully validated which has the main advantage that it can be located inside the aircraft.
"The ILDAS system has been validated on a real aircraft, but on the ground only," adds Mr Zwemmer. "To be ready for real-life applications, ILDAS needs to prove itself in a real airborne environment, and measure actual lightning strikes attached to the aircraft."
He admits, however, that it is very difficult to provide such an environment as pilots are not willing or allowed to deliberately fly into an environment in which an aircraft is likely to encounter lightning strikes. The next step for the ILDAS team is to find a solution to this problem, now that the project has ended.
"We are currently co-operating with Airbus to put an ILDAS system in test aircraft for this purpose," confirms Mr Zwemmer.
After successful in-flight verification of the system, the intention is to develop an extensive business case study to ensure that the ILDAS systems can be applied to operational fleets as cost-effectively as possible.
Besides the ground tests, the ILDAS team also investigated a database concept dedicated to storing and assessing the measured and deduced lightning data. This database will be an asset in itself, suggests Mr Zwemmer, enabling subsequent exploitation of results.
The recorded data from lightning strikes can be downloaded into the database, providing an accurate assessment of the severity of any strike sustained rapidly after the event. Immediate knowledge of the strike severity will give airlines an indication of the required level of post-strike inspection and maintenance to be done, saving both down-time and cost.
Further development of the database concept is likely to take place in future ILDAS projects, according to Mr Zwemmer.