The Federal Aviation Administration has mandated new restrictions on wind conditions in which operators of Gulfstream G500s and G600s are permitted to land.
The agency released an airworthiness directive (AD) on 6 May that responds to a second hard landing event that happened on 4 April.
The AD requires operators to adopt flight manual updates recently released by Gulfstream.
Both hard landings involved erroneous activation of the jets’ angle-of-attack “limiter” function (also called the alpha limiter), which is designed to prevent stalls.
The AD sets the maximum wind speed in which pilots of G500s and G600s are permitted to land at 15kt (28km/h), including gusts, the document says.
Additionally, it prohibits landings if maximum wind gusts exceed 5kt, and it requires pilots add 10kt to their landing reference speed.
The order is to take effect on 9 May and applies to 120 jets registered in the USA, it says.
The 4 April hard landing followed a similar event that occurred on 6 February 2020, according to the FAA.
“As in the first event, the alpha limiter engaged during the landing flare in unstable air, resulting in a high-rate-of-descent landing and damage to the airplane,” says the order.
Both hard landings occurred after the system erroneously activated due to “rapid, large and oscillating pilot control inputs near approach reference speeds, induced by unstable atmospheric conditions and gusty winds”, the FAA says.
As a result, AOA Limiter “overrode the pilot pitch control inputs”, it adds.
The FAA previously addressed the problem with AD in 2020. That order also limited wind conditions in which G500s and G600s could land, though those limits were less strict than in the latest AD.
Gulfstream notified G500 and G600 operators of the latest flight manual updates in a 29 April letter.
The company says it expects this year to release a software fix that will allow the new restrictions to be lifted.
“Gulfstream is and has been working closely with the FAA on a software update for the G500 and G600 to remove published operational landing limitations in gusty wind (>15 knots) conditions,” the company tells FlightGlobal on 3 May.
“Company testing of this update has been completed and we anticipate FAA approval and subsequent deployment later this year,” it adds.