Flight Data Recorders

By Joe White
Director, Engineering
Air Transport Association
March 2006

A Description of Recorders

All large commercial airliners are equipped with two types of devices to record information for the purpose of investigating accidents and incidents. The cockpit voice recorder (CVR) records intercom and radio communications of the flight crew, the aural warnings of flight systems, and the sounds of the cockpit environment. The other so-called “black box” is the flight data recorder (FDR), which chronicles the airplane’s speed, position, altitude, and a number of other flight parameters. Federal Aviation Regulations (eg, 14 CFR 121) require operators of commercial airplanes to carry and use these recording devices.

The Uses of Flight Data Recorders

Although FDRs are designed for use in an accident investigation, they provide no direct contribution to the safety of the airplane on which they are carried. The benefits derived are indirect, having stemmed from previous accidents or incidents and resulting in improvements to aircraft design, maintenance or flight procedures. Airlines are developing ways to use the growing volumes of FDR data, and other data recorded during routine flights, to prevent accidents and incidents before they happen. The Flight Operations Quality Assurance (FOQA) program, for instance, can analyze daily operations for human errors and other problems. In cooperation with manufacturers, operators may also analyze flight data to assess the health of an airplane, including its engines and components. The quality of data that is increasingly available may allow the detection of symptoms long before their cause would otherwise become apparent. This early detection could direct maintenance to a problem area before the failure of critical equipment.

The Capabilities of Flight Data Recorders have Grown

Early FDRs used analog technology and recorded data on metal foils using styli that were driven by electrical voltages proportional to the magnitude of the variables they tracked, much like a seismograph. Modern FDRs record data in a digital format on continuous-use magnetic tapes or other digital storage devices. Digital FDRs, or DFDRs, are capable of recording much more information than analog FDRs, and digital technology is continuously increasing the memory of digital storage devices. Taking advantage of this growth in capacity, airplane manufacturers have, in recent years, installed an increasing number of sensors throughout their airplanes, in order to record increasing numbers of flight parameters for longer periods of time. Manufacturers have hardened DFDRs to survive an accident with useable data, offering great improvements over early FDRs.

Requirements for the Use of Flight Data Recorders have been Expanded Frequently

Regulation amendments have mandated more capable recorders as technology has made them available. Initially, the Federal Aviation Administration (FAA) required that airplanes designed and “type certificated” prior to September 30, 1969, record six flight parameters: altitude; airspeed; heading; vertical acceleration; time of day; and the relative time of radio transmissions to and from air traffic controllers. Airplanes certificated after that date were required to record a total of 11 parameters, adding to the list: pitch attitude, roll attitude, longitudinal acceleration, control-column position, and engine thrust indications.

The FAA subsequently required that, after May 25, 1989, turbine-powered commercial airplanes have DFDRs capable of recording 25 hours of data. Those certificated after September 30, 1969, or manufactured after May 26, 1989, had to record 17 parameters on any flight after May 25, 1994. The six additional parameters included: pitch trim position; control wheel position; rudder pedal position; position of each thrust reverser; trailing-edge flap position; and leading-edge flap position. FAA also increased to 29 the number of parameters required in airplanes having digital data systems, or manufactured after October 11, 1991.

Current Regulations for Flight Data Recorders

On July 17, 1997, FAA adopted the regulations to again increase the minimum number of parameters that FDRs must record. Under this “97 rule”, airlines were required to modify, by August 20, 2001, airplanes manufactured before October 12, 1991, to digitally record either 18 or 22 parameters, depending on whether or not the plane was equipped with a flight data acquisition unit. By the same deadline, airlines modified newer airplanes to record 34 parameters. Airplane manufacturers modified airplanes manufactured after August 18, 2000, to record 57 parameters, and airplanes made after August 19, 2002, must record 88 parameters. These parameters are derived from scores of sensors imbedded throughout the airplane -- over 1,100 sensors are needed in some models to collect 88 parameters. Collectively, this array of sensors reads not only the status of key data items, such as altitude, but documents the overall performance of systems, including: engines; navigational aids; warning systems; hydraulic systems; electrical systems; and flight controls. Current FDRs must retain the most recent 25 hours of flight data. FAA estimated that the modifications of airplanes already in service, as required by the provisions of the “97 rule”, cost the industry $309 million.

Current Capabilities of Flight Data Recorders

The net effect of the periodic upgrading of FDR regulations is that, depending on the age of the airplane, US commercial airliners currently record a minimum of 18, 22, 34, 57, or 88 data parameters. As older airplanes are retired, the lesser minimums will, in effect, expire.

Current Initiatives for Expanding the Use of Flight Data and Cockpit Voice Recorders

In view of advancing technology and accidents and incidents investigation needs, the National Transportation Safety Board (NTSB), the FAA, and the industry periodically evaluate the need for further improvements to recording devices. The FAA recently proposed a regulation that would require that FDRs record data link communications, that would require an independent source of electrical power (eg, a battery) for CVRs, and that cockpit voice recorders record the most recent two hours of voice communications. FAA recently proposed a rule that would increase the number of parameters that monitor the rudder system of Boeing 737 airplanes.

Last updated: 10/6/2006