Following an incident involving a Singapore Airlines (SIA) Airbus Industrie A340 over Australia, the aircraft manufacturer says that it is to put switch-guards over engine hydraulic-valve controls in the A340 cockpit.
Sudden pitch changes caused by an incorrect switch selection by the crew injured 11 people, according to the Australian Bureau of Air Safety Investigation (BASI).
The mechanical guards, which will have to be flipped up to operate the pushbutton switches, will cover the four overhead-panel switches controlling output from the aircraft's four main engine-driven hydraulic pumps. The aircraft's flight-control actuators are hydraulically powered.
The incident, on 5 December, 1996, occurred at 39,000ft (12,000m) on a Singapore-Sydney SIA flight when the crew discovered an 800kg lateral fuel imbalance during pre-descent checks. They intended to correct this by opening all four fuel crossfeed valves to transfer fuel as required. Instead, they accidentally closed off output from all four hydraulic pumps, according to a BASI preliminary report.
This caused a loss of hydraulic-system pressure and autopilot disconnection. The aircraft suddenly pitched up 8í and stalled before being recovered by the crew, which had been alerted to its error by the electronic centralised aircraft monitor.
Hydraulic-, electrical- and fuel-system controls and indicators are each grouped separately on the central overhead panel.
The four hydraulic valve switches are about 170mm higher up the panel than those for fuel crossfeed, but both sets of switches are of the same design.
Airbus says that this type of incident has never happened before in either an A330 or an A340. It adds that its move to install guards is a part of its "pro-active" stance on cockpit safety.
Source: Flight International
