Following its investigation into a commuter plane crash last year in North Carolina, the NTSB said on Thursday that airlines should at least periodically make passengers step on a scale.
The safety board also recommended the Federal Aviation Administration require improvements to training, oversight and procedures for maintenance personnel.
The crash of US Airways Express Flight 5481 at Charlotte-Douglas Airport killed 21 people, the deadliest U.S. aviation accident in nearly 2½ years.
The Beech 1900, operated by Air Midwest, was virtually uncontrollable because of two fatal mistakes, the safety board concluded.
First, the airline's guidelines for estimating the weight of passengers and baggage were inaccurate. The pilots, therefore, didn't realize the plane's rear section was too heavy.
Second, mechanics had improperly rigged cables connected to the elevator, the tail flap that controls the up-and-down direction of the aircraft's nose. The errors meant the elevator's downward motion was restricted to half its normal range, according to the NTSB.
Without a fully maneuverable elevator, the pilots couldn't force the nose of the plane down to compensate for its heavy tail, investigators said.
As a result, the plane pitched sharply upward just seconds after takeoff for Greer, S.C., then fell from the sky.
Soon afterward, the FAA ordered airlines to weigh some of their passengers to determine the accuracy of current guidelines — for example, adults in winter were calculated to weigh 185 pounds on average.
The survey showed what many suspected: Passengers and their bags had gotten heavier. The FAA issued temporary guidelines adding up to 10 pounds to its estimate for passengers and 5 pounds to checked luggage.
"The FAA did a test, if you recall, after this accident where they did actually weight passengers for a period of ... one or two months, and I don't know that there was any public outcry over that," NTSB member Carol Carmody told CBS radio station WBZ-AM. "I think where safety's concerned, the traveling public always wants to do the right thing."
The NTSB recommended the FAA go further, requiring airlines operating planes with 10 or more seats to weigh passengers periodically to determine when they might be heavier — for example, in December when they wear heavy coats and carry presents.
The FAA is working on that. Since June, a committee has been examining the average weights of passengers and baggage and how they vary according to season or geography.
Debby McElroy, Regional Airline Association president, said her group is working with the FAA on the weight and balance issues identified by the NTSB.
"We agree that further study is necessary, to ensure that air carrier weight and balance programs provide the highest level of safety," McElroy said.
The committee is expected to make recommendations next month.
NTSB investigators also found flaws in the way mechanics were trained and supervised, how their work was checked and how Air Midwest controlled the quality of its maintenance. Those problems led to the improperly rigged elevator cables on the Charlotte flight.
As part of a series of recommendations on maintenance, the NTSB said the FAA should require that work on key flight control systems, including elevator cables, be checked upon completion.
FAA spokeswoman Laura Brown said the agency already is working on the issues raised by the investigation.
Two Democratic members of the House Transportation and Infrastructure Committee, James Oberstar of Wisconsin and Peter DeFazio of Oregon, asked the Transportation Department's inspector general to report on whether outsourced maintenance work affects airline safety.
Air Midwest contracted maintenance to Raytheon Aerospace (now known as Vertex Aerospace), which hired mechanics from Structural Modification and Repair Technicians Inc.