Transponder modifications to ensure rapid activation and continuous operation of the hijack alert code have been proposed by the US Federal Aviation Administration. The notice of proposed rulemaking (NPRM) results from decisions taken after the 11 September terrorist attacks, in which none of the flightcrews was able to enter the code and three of the four aircraft ceased replying to secondary radar interrogation.
The proposed rule requires single-action activation of the "7500" code, via a switch or button that is guarded to prevent unintentional triggering. The rule also requires measures to prevent the code being changed, the transponder being switched to standby or the power supply being interrupted. On activating the hijack code, power would be removed from electrical breakers in the cockpit and transferred to remotely mounted breakers not accessible from the flightdeck.
The proposed compliance date is 29 March 2005, and the rule would affect almost 7,400 passenger and cargo aircraft operated by US carriers, at a cost of about $88 million. The NPRM asks for comments on whether the rule should include business and charter operators.
The FAA expects most operators to comply by uploading new software that would lock the transponder into continuous operation. Operators will be allowed to comply by installing a third, dedicated transponder remotely, but this will require a means to inhibit replies from the other transponders once activated, the FAA says.
Source: Flight International
