 The first bulb was thus presumed to have gone inoperative some time before the day of the flight, while the second bulb broke during Flight 933.The NTSB therefore advised the Federal Aviation Administration to articulate means to avoid similar compromised fail-safe designs in the future.Both pilots had minimum-descent altitude light warnings, which were presumed to have given a visual warning, but because of the work overload, neither pilot directed his attention to these alerts.