Protecting airports from lightning strikes

For airports and the airlines that serve them, few weather phenomena are as disruptive as electrical storms. Tom Batchelor looks at the risks and the remedies

From structural damage to disabled onboard electrical systems and the threat of injury or death to those on the ground, a lightning strike can be dangerous and costly. And with more than two billion bolts detected worldwide in any given year, it is a risk factor that the aviation industry cannot avoid. Indeed, with climate change becoming an ever more pressing problem, the challenges posed by lightning and the severe weather that accompanies it are only likely to worsen.

Vast sums of money continue to be spent adapting infrastructure to help withstand electrostatic pulses, and to predict when the next big storm will hit.

Thunderstorm Manager
Thunderstorm Manager is a cloud-based software application that can be accessed from anywhere using a computer, laptop or mobile device with an internet connection Vaisala

In 2018, the UK’s Stansted Airport was brought to a standstill by lightning after the fuelling system was struck, leaving planes unable to take off. More than 100 departures and arrivals were delayed or cancelled, resulting in significant costs for the airport’s numerous operators. In 2013, lightning hit the air-traffic control tower at Baltimore-Washington International Airport, injuring a worker and leading to the temporary closure of the tower.

Stand out incidents like those grab headlines, but disruption to airport and airline operations caused by lightning is a daily occurrence. On a single day in August 2021, a “prolonged severe weather event” lasting nine hours upended flight schedules and triggered nearly 100 diversions at Dallas-Fort Worth Airport in Texas, while at Florida’s Miami International Airport lightning shut down ground operations for two hours.

Over the course of 2020, Earth Networks – which runs a weather data network providing early lightning warnings to airports as well as schools, sports teams and government agencies – detected more than 400 million in-cloud and cloud-to-ground lightning pulses within the continental US alone. This was actually a fall of 15% compared with 2019. And more than 31.5 million of those pulses were cloud-to-ground, which poses the greatest headache for airports, representing 7% of all lightning activity.

The implications for aircraft
Lightning is at best disruptive and at worst deadly for passengers and crew travelling by air. Electrical storms can affect avionics systems, particularly compasses, trigger temporary pilot incapacitation by way of flash blindness, and may even lead to an engine shutdown. On rare occasions, they can also cause structural damage, such as holes in the radome or tail fin, marking the entry or exit point of the lightning bolt. A helicopter can itself trigger an isolated lightning strike: it acquires a negative charge during flight, and when the helicopter approaches an area that is positively charged, a lightning strike can occur.

In 2019, an Aeroflot Sukhoi Superjet 100-95 performing a domestic flight from Moscow Sheremetyevo International Airport to Murmansk in Russia crashed during an emergency landing after encountering an electrical storm. A lightning strike was reported to have first wiped out the onboard radio communications and during the landing the aircraft veered off the runway and burst into flames. A total of 41 people died in the incident.

Greater risks on the ground
Since the fuselage of an aeroplane acts like a Faraday Cage (an enclosure used to block electromagnetic fields), passengers are generally protected during the frequent (about one in every 1,000flight hours) lightning strikes that involve aircraft. In fact, the dangers presented by lightning strikes to those on the ground can be greater than those posed to airborne objects.

Ground handling staff are more exposed to the elements, and the vast fuel stores and active refuelling of aircraft make for a higher risk. When an electrical storm is detected in the vicinity of an airport, typically within 5km (3 miles), suspension of certain airside operations is advisable, including pushback, fuelling and boarding and disembarking passengers.

Being able to detect lightning is an important part of an airport’s activities. Much of the danger associated with lightning comes not from the electrical discharge itself but from the accompanying conditions: intense precipitation, severe icing, wind shear, turbulence and strong wind gusts – all of which can be hazardous to aircraft, especially those approaching or departing airports in critical stages of flight.

Nathan Neal, marketing director at Biral, a Bristol-based company which designs and manufactures meteorological sensors for the aviation industry as well as offshore platforms and wind energy, said a plane being struck by lightning was “actually not a huge issue”.

Speaking to AIR International, he explained: “The bigger problem, especially for inbound and outbound flights, is actually the fact that the associated thunderstorm is quite a dangerous thing to fly through because of the windshear, up-draughts, frosting and freezing. The lightning is just a damn good indication of what it is above you. Although certainly in a light aircraft, you don't want to be flying through a thunderstorm.” He added: “On the ground, you've got baggage handling guys, they're all outside and potentially they're at risk. Refuelling is a hazardous practice on any day of the week, but you don't want lightning coming down onto the tarmac while you're refuelling a plane – that could be catastrophic. Generally refuelling would be suspended as soon as there is any lightning in the area.”

So what can airports do to protect staff, travellers and aircraft from lightning strikes? Most pay for accurate lightning detection services that provide real-time information about where electrical storms are developing and in what direction they are moving. Audio and visual warnings can also be provided on the apron in the form of horns and flashing lights. One provider, the Earth Networks Total Lightning Network (ENTLN), has 1,800 sensors and a team of lightning scientists and meteorologist experts on hand 24/7.

The scale of the problem
Leading players in the aviation industry rely on the network’s data supply to protect people and infrastructure, something that is particularly important in parts of the world where lightning strikes pose a regular threat to the smooth running of airports and airlines alike. Last year, the ENTLN issued more than 29,000 'Dangerous Thunderstorm Alerts', with the highest concentrations in the Great Plains and southeastern United States. “Based on our network records, 2020 represents a historic reduction in lightning activity in the US overall,” said Mark Hoekzema, chief meteorologist at Earth Networks. “Although the southeast US saw more lightning, Florida continued its downward trend and the western and southwestern states were locked in a persistent drought. By contrast, 2019 experienced a large-scale atmospheric teleconnection called the Madden-Julian Oscillation (MJO), which caused a more active than normal storm season, specifically in the Great Plains lightning-prone region.”

Incheon Biral BTD
A Biral BTD300 in operation at South Korea’s Incheon International Airport Biral

With contracts to supply information for airlines operating in approximately 150 airports worldwide and coverage in more than 100 countries, Earth Networks boasts the “largest global hyperlocal weather network” and says its ability to monitor in-cloud lightning sets it apart from other networks. Detecting in-cloud lightning enables faster lightning alerts that warn of other forms of severe weather including tornadoes, downbursts and hail. Subscribers to the service can request that lightning alerts are sent when the electrical discharges are detected within a certain radius from the airport. “There is a standard radius of about five miles,” Randy Smith, Earth Networks’ homeland security specialist, told AIR International. “But it's not set in stone. United Airlines starts receiving lightning alerts for an airport at 25 miles, but they may not act until it is 5 miles away, for example. Some airports don't act until it's 3 miles away. It all depends upon what their operations dictate.”

A costly predicament
Why is there such demand for this service? One reason is safety, and the other is money. “The information we provide allows operators to do two things,” explained Smith. “One is to keep their outdoor people safe. The other thing is by having better information, they can reduce their downtime when their planes are not flying. The more accurate your data is, the more accurately you are going to be able to manage your schedule. You may be able to eliminate the suspension of flights by five or 10 minutes. That's a huge amount of money to an airline, not least avoiding the costs of parking at a major hub. We're talking potentially millions of dollars an hour.”

Hong Kong was one of the first major airports worldwide to adopt an Airport Lightning Warning System (ALWS). Connected to local field mills (described in more detail later in this article) and a separate detection radar system, the ALWS consists of two warning types: amber, which does not affect aircraft operations, for when the lightning is detected within 7km of the airport and airport staff should stop non-essential activities in open areas; and red, when a lightning strike is detected at the airport or the threat of a lightning strike is very high. Under this scenario, all ramp activities including baggage handling and aircraft refuelling must stop immediately.

Detection techniques
There are two traditional methods used to detect lightning. The first, known as a lightning network system, relies on a number of discrete sensors commonly stationed in rural areas that detect the electromagnetic pulses that are generated by a storm. The sensors can be hundreds of miles apart but still capable of locating a strike accurately to within 100-200 metres.

This method is employed by large meteorological organisations such as the UK’s Met Office, which has an ATDnet (Arrival Time Difference Network) system consisting of around ten lightning outstation sensors located across Europe. Together, they can determine the time and location of strikes across a large geographical area. ATDnet can also detect lightning from outside Europe, although its accuracy and sensitivity diminishes significantly at longer ranges. So while the lightning stroke location for the British Isles and Western Europe is accurate to around 1-2km, this drops to 5-10km at the eastern, northern and southern edges of Europe, and up to 60km for lightning strikes in South America.

The alternative method relies on field mills that detect the charge in the atmosphere then determine the rate of change of that charge. They detect the charge in the atmosphere increasing, which when analysed pinpoints the location and timing of approaching lightning – though they cannot be too far from the storm (no further than around 10km). Neal said field mills were popular in some countries because they were cheap and easy to deploy in their thousands, but they also suffer from interference and false alarms since they detect everything in the atmosphere.

Experts at Biral have developed a novel sensor that “takes the best” from each of those two types of equipment. The BTD-300 Thunderstorm Detector can reliably warn of the presence of all forms of lightning to a range of 83km by detecting the charge dissipation every time the lightning strike comes to ground. “We are measuring the charge neutralisation of the lightning strike,” explained Neal.

“For an airport, the big benefit that we offer is that because we are measuring the atmospheric charge and dissipation of the charge [it] means we can give advance warnings of the threat of overhead lighting, which is obviously the critical bit because it's going to come to ground on your site, rather than just a warning of lightning approaching in the distance. That's the big advantage over other pieces of equipment, and it offers five, ten or even 15 minutes’ warning.”

The impact of climate change
One place where you can be assured of regular lightning disruption is Lake Maracaibo in Venezuela. With thunderstorms on approximately 150 nights a year and an average of 28 lightning strikes per minute, it is the place that receives the most lightning strikes. And it is parts of the tropics such as Venezuela where storms are expected to become even more disruptive because of climate change, which is having an impact on the severity and frequency of extreme weather. Experts believe that a warmer planet may actually lead to fewer lightning storms overall, but the storms that do develop will be more intense, with an overall increase in the number of lightning strikes. Neal explained: “If the climate warms it means that you get more evaporation from the seas, you put more water into the atmosphere, and because the atmosphere is warmer it can actually hold more water, so the atmosphere is more energetic, and by pure physics it means that there will be heavier thunderstorms.” Only time will tell what impact this will have on airline and airport operations in the regions worst affected by lightning, but with improving forecasting and detection technology the risks to all involved can at least be minimised.

Lightning risk index
Finland-based weather expert Vaisala has produced a lightning risk index (see page 85) to measure how much each airport is impacted by lightning. Calculated by multiplying the airport’s total number of take-offs and landings by the lightning density, the index gives airlines and airports an insight into where their operations are most likely to face disruption.

C123 Base
In 2020 the Earth Networks Total Lightning Network issued more than 29,000 ‘Dangerous Thunderstorm Alerts’ Earth Networks

For US operators, the risk register includes clusters of airports in Texas and Florida. Dallas-Fort Worth International Airport tops the list, followed by Orlando International Airport, George Bush Intercontinental Airport in Houston, and Miami International Airport. Among the airports at the bottom of the index are hubs along the US west coast.

“With personnel loading and unloading baggage and cargo, fuelling aircraft, and preparing for the next arrival or departure, lightning is a potentially significant safety threat on the tarmac,” said Chris Vagasky, Vaisala’s meteorologist and lightning applications manager.

“Lightning strikes to the runway can also cause damage and delays. Understanding the lightning risk at your airport is the first step in preparing for how lightning can impact your operations.”

To get a sense of the lightning risk for airports globally, Vaisala uses a slightly different metric: passengers flown rather than take-offs and landings. Using data from 2019 (2020 data was not included due to the pandemic), it found that there were four airports globally which were higher up the Airport Lightning Risk Index than any of the US locations mentioned: Kuala Lumpur International Airport, Changi Singapore International Airport, Guangzhou Baiyun International Airport (in southern China) and Suvarnabhumi International Airport in Bangkok, Thailand. “These airports get a lot of thunderstorms because they are in subtropical and tropical climates,” Vagasky told AIR International.

Ethiopian Airlines lightning strike
When an aircraft suffers a lightning strike, it must undergo a maintenance check for any structural or other damage.

A less conventional procedure is an exorcism by Voodoo priests – but that is exactly what happened to an Ethiopian Airlines Boeing 787-8 Dreamliner which was struck shortly before a flight to New York’s Newark airport from Lomé Airport in Togo. The front of the aircraft’s left wing was hit by lightning while it was taxiing at Lomé-Tokoin International Airport in June this year, forcing the airline to transfer passengers to another plane. After a request to carry out the purification ceremony was reportedly made to local officials, the eight-year-old jet underwent the spiritual procedure, apparently to ease any fears among future travellers that the plane was somehow cursed. Photos shared on social media showed priests sprinkling water on the plane from the attached boarding stairs.

Colonel Dokisime Gnama Latta, the director-general of Togo’s National Civil Aviation Agency (ANAC), attended the ceremony. “Everything was done to facilitate their task,” he told Togolese media. “The voodoo priests have their traditions. They told us that in cases like that, you have to come and do a little ceremony to exorcise the place so that it does not happen again.” Colonel Latta added: “They didn’t get on the plane, they just climbed the stairs to do their ceremony. The plane had no problem. The plane was not struck in the air as some say. No person on board the aircraft was injured. After the incident, all passengers were transferred to another Ethiopian Airlines flight.” The aircraft underwent an inspection before returning to service.