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Lightning is an atmospheric discharge of electricity. A lightning strike can be very distressing to passengers and crew but damage to an aircraft in flight which is sufficient to compromise the safety of the aircraft is rare.
Lightning occurs as a result of a build up of static charges within a Cumulonimbus (Cb) cloud, often associated with the vertical movement and collision of ice particles (Hail), which result in a negative charge at the base of the cloud and a positive charge at the top of the cloud. Beneath the cloud, a "shadow" positive charge is created on the ground and, as the charge builds, eventually a circuit is created and discharges takes place between the cloud and the ground, or between the cloud and another cloud. An aircraft passing close to an area of charge can initiate a discharge and this may occur some distance from a Thunderstorm.
Lightning strikes on aircraft commonly occur within 5,000 feet of the freezing level.
Lightning is accompanied by a brilliant flash of light and often by the smell of burning, as well as noise. A lightning strike can be very distressing to passengers (and crew!) but significant physical damage to an aircraft is rare and the safety of an aircraft in flight is not usually affected. Damage is usually confined to aerials, compasses, avionics, and the burning of small holes in the fuselage. Of greater concern is the potential for the transient airflow disturbance associated with lightning to cause engine shutdown on both Full Authority Digital Engine Control (FADEC) and non-FADEC engines with close-spaced engine pairs.
Lightning may also occur in Volcanic Ash clouds formed in the immediate vicinity of eruptions because the vertical movement and collision between solid particles within the cloud generates static charges.
The Following map shows the uneven distribution of lightning strikes across the globe. The data is from space-based sensors.
- Aircraft Damage. Structural damage to aircraft from Lightning strikes is rare and even more rarely of a nature that threatens the safety of the aircraft. Nevertheless, there have been many incidents of lightning strikes leaving puncture holes in the radomes and tail fins of aircraft (entry and exit holes) and damage to control mechanisms and surfaces (see Further Reading).
- Crew Incapacitation. Momentary blindness from the lightning flash, especially at night, is not uncommon.
- Interference with Avionics. A lightning strike can effect avionics systems, particularly compasses.
- Engine Shutdown. Transient airflow disturbance associated with lightning may cause engine shutdown on both FADEC and non-FADEC engines on aircraft with close-spaced engine pairs. see separate article on Lightning Strike Risk to Engines.
- Avoidance. Standard advice to pilots is to remain at least 20 nautical miles displaced from any Cumulonimbus (Cb) cloud. The dangers from Turbulence, Low Level Wind Shear, and In-Flight Icing associated with Cumulonimbus clouds are far greater than the threat of Lightning.
- If flying in the vicinity of cumulonimbus clouds, or lightning is seen close to the aircraft, then review manufacturers guidelines for action to be taken in the event of a lightning strike. If the aircraft is equipped with gyro-magnetic compasses, it may be recommended that one of the compasses is selected to gyro while there is a risk of lightning.
Accident & Incident Reports Including Lightning as a Factor
- AS3B, en-route, northern North Sea UK, 2008 (On 22 February 2008, a Eurocopter AS332 L2 Super Puma flying from an offshore oil platform to Aberdeen was struck by lightning. There was no apparent consequence and so, although this event required a landing as soon as possible, the commander decided to continue the remaining 165nm to the planned destination which was achieved uneventfully. Main rotor blade damage including some beyond repairable limits was subsequently discovered. The Investigation noted evidence indicating that this helicopter type had a relatively high propensity to sustain lightning strikes but noted that, despite the risk of damage, there was currently no adverse safety trend.)
- D228, vicinity Bodø Norway, 2003 (On 4 December 2003, the crew of a Dornier 228 approaching Bodø lost control of their aircraft after a lightning strike which temporarily blinded both pilots and damaged the aircraft such that the elevator was uncontrollable. After regaining partial pitch control using pitch trim, a second attempt at a landing resulted in a semi-controlled crash which seriously injured both pilots and damaged the aircraft beyond repair. The Investigation concluded that the energy in the lightning had probably exceeded certification resilience requirements and that up to 30% of the bonding wiring in the tail may have been defective before lightning struck.)
- A332, Perth WA Australia, 2014 (On 26 November 2014, an Airbus A330-200 was struck by lightning just after arriving at its allocated stand following a one hour post-landing delay after suspension of ramp operations due to an overhead thunderstorm. Adjacent ground services operatives were subject to electrical discharge from the strike and one who was connected to the aircraft flight deck intercom was rendered unconscious. The Investigation found that the equipment and procedures for mitigation of risk from lightning strikes were not wholly effective and also that perceived operational pressure had contributed to a resumption of ground operations which hindsight indicated had been premature.)
- SB20, vicinity Sumburgh, UK 2014 (On 15 December 2014, the Captain of a Saab 2000 lost control of his serviceable aircraft after a lightning strike when he attempted to control the aircraft manually without first disconnecting the autopilot and despite the annunciation of a series of related alerts. The aircraft descended from 4,000 feet to 1,100 feet at up to 9,500 fpm and 80 knots above Vmo. A fortuitous transient data transmission fault caused autopilot disconnection making it possible to respond to EGPWS 'SINK RATE' and 'PULL UP' Warnings. The Investigation concluded that limitations on autopilot disconnection by pilot override were contrary to the type certification of most other transport aircraft.)
- E145, vicinity Manchester UK, 2001 (On 25 September 2001, an Embraer 145 in descent to Manchester sustained a low power lightning strike which was followed, within a few seconds, by the left engine stopping without failure annunciation. A successful single engine landing followed. The Investigation concluded that the cause of failure of the FADEC-controlled AE3007 engine (which has no surge recovery logic) was the aero-thermal effects of the strike to which all aircraft with relatively small diameter fuselages and close mounted engines are vulnerable. It was considered that there was a risk of simultaneous double engine flameout in such circumstances which was impossible to quantify.)
- Engine Malfunction Caused by Lightning Strikes, UK CAA AIC 29/2004 (Pink 64), April 29 2004
- Aircraft Lightning Protection Handbook, FAA, 1989
- Lightning Direct Effects Handbook, E. Rupke, March 2002
- Overview of Lightning Protection of Aircraft and Avionics, R. Majkner, Sikorsky, October 2003
- Lightning Strikes: Protection, Inspection, and Repair, G. Sweers et al., Boeing AERO 2014 QTR4, 2012
- Direct Effects of Lightning on Aircraft Structure: Analysis of the Thermal, Electrical and Mechanical Constraints, L. Chemartin et al., Aerospace Lab 05/09 Issue 5, December 2012
- Study of Effects of Lightning Strikes to an Aircraft, N. Petrov et al., in 'Recent Advances in Aircraft Technology', edited by R. K. Agarwal, 2012