The black boxes (search) key to determining the causes of aircraft crashes will have to hold more data and have a more reliable power supply under a plan outlined Thursday by the Federal Aviation Administration.

However, the FAA (search) rejected a recommendation from the National Transportation Safety Board that aircraft be required to have video cameras in the cockpit. Some pilots have expressed concerns about invasion of privacy and said the constant presence of a camera could make it harder to do their jobs.

The NTSB, which investigates crashes, has long urged the FAA to adopt stricter requirements for the boxes. Safety investigators have cited the boxes' failure to yield useful information about several fatal airliner accidents, including the 1998 crash of Swissair Flight 111 off the coast of Halifax, Nova Scotia, and the 1999 crash of Egyptair Flight 990 off the Massachusetts coast.

In those two accidents, the black boxes shut off before the planes crashed.

The new rules would require cockpit voice recorders, which record pilots' conversations, to retain at least two hours of audio and have a 10-minute backup power source. They are now only required to record 15 to 30 minutes of sound and don't have to have backup power.

Cockpit voice recorders (search) that use magnetic tape would no longer be permitted because they're not as reliable as digital recorders and more vulnerable to damage.

Flight data recorders, which record the movement of cockpit controls, would sample data more often and retain 25 hours of information. Now, they have to measure data every second in airplanes; the proposal would require sampling every 1/16th of a second. For helicopters, they will have to sample four times a second rather than the two times per second now permitted.

"Good data is often the Rosetta stone to deciphering what happened in an aircraft incident and what could happen in an accident," FAA Administrator Marion Blakey said.

The public will have a chance to comment on the proposal, which is expected to take effect by the end of next year.

The FAA estimates the new rules will apply to about 9,600 aircraft with 10 or more seats and cost the aviation industry $256 million.

New aircraft must have black boxes — which are actually orange — that meet the new standards two years after the rule is in force.

Aircraft operators must retrofit existing planes with cockpit voice recorders that meet the standard four years after the rule takes effect.

John Hickey, the FAA's director of aircraft certification, said the FAA isn't proposing to retrofit aircraft with new flight data recorders because the vast majority already meet the rule's requirements.

The pilots' largest union said in a statement that it welcomed the changes but wanted the FAA to set stronger standards for protecting flight data. Pilots are concerned that cockpit voice recordings are used for purposes other than enhancing aviation safety — such as litigation or disciplinary action.

"We know that recorded safety information has been misused and abused in the past and that these practices continue today," said Terry McVenes, executive air safety chairman of the Air Line Pilots Association, International.