(
opex360 (fr), nov.23)
Despite update, Pentagon maintains F-35A flight restrictions in stormy weather
On 28 August 2020, F-35 fighter-bombers from the Dutch Air Force [Koninklijke Luchtmacht, Klu] were to join the NATO exercise 'Allied Sky', which aimed to demonstrate allied solidarity by escorting six US B-52H Stratofortress strategic bombers over Alliance territory.
However, as the weather forecast predicted a stormy depression for the Benelux countries, the F-35As remained in Leeuwarden... due to flight restrictions forbidding them to approach within 40 km of a storm. Indeed, due to a problem detected in their OBIGGS [On Board Inerting Gas Generation System], these aircraft were potentially vulnerable to lightning.
The OBIGGS problem had been detected a few weeks earlier during maintenance on F-35A aircraft at Hill Air Force Base in Utah.
For aircraft, lightning is not necessarily the most dangerous phenomenon, provided they have an OBIGGS, which eliminates the risk of fire or explosion should they be struck in their tanks.
The principle of such a device is to replace the oxygen in a tank with an inert gas to make the fuel vapours non-flammable.
However, during the operations at Hill, it became apparent that some of the tubes used to circulate the inert gas in the tanks were showing premature wear. This led to flight restrictions again being imposed by the F-35 Joint Program Office [i.e. the F-35 program office at the Pentagon]...
Indeed, this was not the first time the F-35 had experienced a problem with its OBIGGS system. In the early 2010s, it was found that it did not send enough nitrogen into the tanks to make it completely inert. So its manufacturer, Lockheed-Martin, developed a fix, which lifted the flight restrictions in stormy weather.
However, in June 2021, Lockheed-Martin assured the F-35 that the problem was "field related" and the F-35 programme office set about finding a solution. In November of that year, the programme office indicated that it was considering a "hardware change", replacing "a section of tubes and fittings" in the device with a more robust design. At least enough to withstand the vibrations that occur during flight. And in August 2022, a software update, which is supposed to warn the pilot of possible OBBIGS degradation, began to be installed on the F-35A.
Presumably, the other two versions of Lockheed-Martin's fighter-bomber, the F-35B [short take-off and vertical landing] and the F-35C [airborne variant], would also be affected, as they were scheduled to undergo the same modifications last February.
According to Air Force Times, despite the flight restrictions, some F-35s were still struck by lightning. The mishap happened to an aircraft from the 6th Weapons Squadron at Nellis Air Force Base [Nevada] in August 2021. It was classified as a 'Class B' incident, meaning that it caused between $600,000 and $2.5 million in damage. A few days earlier, two US Marine Corps [USMC] F-35Bs suffered the same fate, with damage estimated at $570,000.
In total, according to Laura Seal, a spokeswoman for the F-35 programme office quoted by Air Force Times, the US Air Force and USMC had reported, as of 25 January 2022, that their F-35s had been struck by lightning 15 times, with each incident costing between $25,000 and $570,000 in repairs.
So, even though none of these incidents resulted in the loss of a pilot, the Pentagon is not taking any chances... despite the upgrade applied to the F-35A's OBBIGS system... which is, in the end, probably not enough.
"The upgrade will improve but is not sufficient to remove the lightning restrictions," a spokesman for the F-35 programme office told Breaking Defense, after "additional findings earlier this year". These restrictions will be lifted when all safety issues are resolved or mitigated to an acceptable level," he said. He did not wish to say more, "for operational security reasons". /deepl