Flight Data Recorder (FDR): Meaning, Difference, Operation, Parts, Location

Flight Data Recorder (FDR), referred to as an Accident Data Recorder (ADR), is a device used to record specific aircraft performance parameters for at least the last 25 hours of operation. Housed within a robust, fire-resistant casing, the unit collects and records data from a variety of aircraft sensors, preserving the recent history of the flight by logging dozens of parameters several times each second. In addition to instructions sent to electronic systems and vertical accelerations, these measurements guarantee investigators have a detailed, survivable account of the aircraft's behaviour.

Expert behind this article

Jim Goodrich

Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.

What is a Flight Data Recorder (FDR)?

A Flight Data Recorder (FDR), known as the "black box," records specific aircraft performance parameters, systems status, and environmental conditions. It records an extensive array of flight data from a variety of aircraft sensors onto a medium designed to survive an accident.

Flight Data Recorder (FDR) is one of the two flight recorders required by ICAO. Together with the Cockpit Voice Recorder it forms the pair of black boxes carried on aircraft. The device continuously registers data-flight path, warnings, and the instructions sent to any electronic systems onto a crash-protected medium that is designed to survive high-impact accidents and fire. Because the recorded information provides insights for accident and incident investigation, the FDR is regarded as the pinnacle of aviation safety technology.

Although popularly called a black box, the recorder is painted bright orange so that investigators can locate it quickly after a crash. The adjective black simply means that the inner workings are opaque to outsiders. The same bright-orange, crash-hardened FDR principle applies to helicopters, which are equipped with a single combined recorder that integrates both flight-data and cockpit-voice functions.

What does a flight recorder do?

A flight recorder is an electronic recording device placed in an aircraft for the purpose of facilitating the investigation of aviation accidents and incidents. It is a device that records the performance and condition of an aircraft in flight, receiving data from aircraft sensors and storing both data and sound. The recorder provides crash-protected memory units and crash-survivable functionality, assuring that information remains intact even after severe impacts.

Flight recorders are an indispensable tool in identifying and addressing the causes and contributing factors of an accident or incident. They support the overall picture of the event, enabling accurate reconstruction of the flight path, voice analysis, and determination of the cause of accidents. By storing cockpit ambient noise, radio communications, and flight crew communications, the recorder helps prevent recurrence of accidents and supports advancement of safety protocols.

Every air vehicle must carry a crash-protected memory unit. The device supports airline safety requirements, certification, compliance, and safety management programs. It serves the ethical necessity to prevent recurrence of accidents and has made a huge contribution to air safety.

A flight recorder's sole duty is to document. It records information aboard the aircraft that can later be used by investigators in the event of an accident. Conclusions drawn from the information prevent future accidents. I regard it as an important and irreplaceable component of aircraft safety.

Jim Goodrich

Pilot, Airplane Broker and Founder of Tsunami Air

What are the types of flight data recorders

The types of flight data recorders include the Flight Data Recorder and the Cockpit Voice Recorder.

The two devices are sometimes packaged together in one combined unit, and such combination recorders are defined by ICAO as combination recorders.

How does a Flight Data Recorder work?

A Flight Data Recorder works by continuously collecting a stream of digital information from aircraft sensors and flight-control computers. Modern recorders store this information in solid-state memory, and manufacturers frequently use data compression techniques to store the data so that more parameters fit into the crash-survivable memory unit designed to withstand extreme conditions. Solid-state recorders also record over old material in a continuous loop, typically preserving the last 25 hours of operation.

The device itself does not contain a GPS receiver. A stand-alone GPS unit allows the black box to know its own location, but the recorder's job is to record flight parameters, not to navigate. Instead, the aircraft's existing navigation data - including latitude and longitude derived from on-board GPS - are among the parameters written into memory. After an accident, the unit is located by its attached underwater locator beacon, which uses an emergency locator transmitter that pulses an ultrasonic signal once immersed. The ULB transmits a signal for 90 days, enabling search teams to hone in on the crash site even if the recorder is buried in silt or wreckage. Thus, the recorder does not actively transmit location during flight but simply preserves the data so that investigators can replay the final moments once the unit is recovered.

When does a Flight Data Recorder start recording?

The FDR does not start recording until the red rotating beacon is switched on, an event that precedes engine start and push-back. From that moment the recorder runs without interruption until the aircraft completes the landing roll at the destination, capturing the entire take-off-to-landing segment demanded by regulation.

What are the components of a Flight Data Recorder?

The components of a Flight Data Recorder are detailed below.

• Power Supply: FDRs run off of a dual voltage power supply (115 VAC or 28 DC) which gives flexibility to be used in a variety of aircraft. The batteries are designed for 30-day continuous operation and have a six-year shelf life.
• Crash Survivable Memory Unit (CSMU): The CSMU is designed to retain 25 hours of digital flight information. The stored information is of very high quality because the unit's state of the art electronics allow it to hold data in an uncompressed form.
• Integrated Controller and Circuitry Board (ICB): This board contains the electronic circuitry that acts as a switchboard for the incoming data.
• Underwater Locator Beacon (ULB): The device, informally known as a "pinger," is activated when the recorder is immersed in water. It transmits an 8.8 kHz acoustic signal for a minimum of 90 days and its range is 13-22 km (8.1-13.7 mi), four times greater than standard ULBs.

Data from the FDR is stored on stacked memory boards inside the crash-survivable memory unit (CSMU). Sensors located throughout the aircraft feed information into the Flight Data Acquisition Unit (FDAU). The FDAU serves as a type of funnel that takes all collected information, puts it in a standard format (normally ARINC 717), and writes it to the FDR. If a Quick Access Recorder (QAR) is installed, the FDAU also routes the same data stream to it. The ELT is the device that sends a distress signal and transmits the position of the aircraft in a crash; the black boxes themselves do not send their position, the ELT does. Most modern FDR systems incorporate an Emergency Locator Transmitter (ELT) to assist in locating the aircraft. For overwater accidents, the cockpit voice recorder includes an Underwater Locator Beacon (ULB). The ULB only sends its position when underwater, transmitting an 8.8 kHz acoustic signal for a minimum of 90 days, its range is 13-22 km (8.1-13.7 mi), four times greater than standard ULBs.

What is the Flight Data Recorder made of?

Modern flight recorders are double wrapped in strong corrosion-resistant stainless steel or titanium. The crash-survivable memory unit consists of a heavy stainless steel shell wrapped within layers of insulating material and covered by an aluminum housing. High-temperature insulation is dry-silica material 1 inch (2.54 cm) thick that provides high-temperature thermal protection. The key element is made of precision alloys, and the stack of solid-state memory cards is surrounded by a thin layer of aluminum. Eliminating moving parts reduces risk of breakage in an accident, and the entire assembly is sheathed inside a multi-layer protective shell.

What are the specifications of a Flight Data Recorder?

A Flight Data Recorder is supplied with airspeed, altitude, and directional data obtained from sources that meet aircraft level system requirements. The FDR records at least 25 hours of flight data and two hours of audio in a continuous-loop solid-state memory, satisfying EUROCAE ED-112 minimum specification and ICAO Annex 6 crashworthiness requirements. Industry specifications demand that the recorder must survive an impact of 3400 g for 6.5 ms, temperatures exceeding 1,000°C (1,832°F) for 30 minutes, and a low-temperature fire for 10 hours. Each recorder container must be bright orange or bright yellow, and an underwater locating device is mounted on or adjacent to the container. The vertical acceleration sensor is rigidly attached within the approved center of gravity limits of the airplane or within 25 percent of the airplane's mean aerodynamic chord. Documentation sufficient to convert recorded data into engineering units and discrete values must be maintained by the certificate holder.

Where is the Flight Data Recorder located?

The Flight Data Recorder is normally installed in the aircraft's tail section, an area identified as the most crash survivable part of the aircraft. Flight recorders are located near the aircraft's tail because experience has shown that the tail area generally suffers the least damage during an accident, giving the best chances of recovering them after an impact. Sometimes the flight data recorder is located in the tail cone that covers the rear of the aircraft, or in the aft cargo hold, or in the ceiling of the galley, yet the precise location depends on the individual plane.

In every case the recorder container must be placed as far aft as practicable, but it need not be outside of the pressurized compartment, and it will not be situated where aft-mounted engines crush the container during impact. Both black boxes are installed in the empennage section, assuring the unit is mounted where structural integrity is most likely to remain intact.

What powers the Flight Data Recorder?

A Flight Data Recorder receives electrical power from a bus that is selected for maximum reliability and that does not compromise service to necessary or emergency loads. In many installations the FDR is connected to an essential bus, a battery bus or an emergency bus. If one of these basic electrical buses is energized the recorder remains active.

To guard against interruption, the forward-installed solid-state recorder is paired with a Recorder Independent Power Supply (RIPS). This internal backup source provides 10 minutes of continuing power if normal aircraft power is lost, so the unit can keep recording during the moments after an electrical failure. The low power demand of modern solid-state technology makes this battery-backed operation practical, eliminating the earlier dependency on engine-driven generators alone.

The flight data recorder is fed first from a reliable aircraft bus and, if that source fails, from its own independent battery, guaranteeing uninterrupted operation without jeopardising emergency functions elsewhere on the airplane.

What are the parameters recorded by a Flight Data Recorder?

Flight Data Recorders (FDRs) record numerous parameters that assess the aircraft's trajectory, attitude, control inputs, and the status of systems. FDRs preserve the recent history of the flight by recording over 1000 parameters collected several times per second. Modern FDRs for air carriers store 88 parameters. By regulation, newly manufactured aircraft must monitor at least eighty-eight important parameters including time, altitude, airspeed, heading, and aircraft attitude. Typical parameters recorded by FDR include pressure altitude, indicated airspeed, heading-primary flight crew reference, the control and actuator positions, engine information, time of day, autopilot engagement status, and manual radio transmitter keying, or CVR/DFDR synchronization reference.

Types II and IIA FDRs record the parameters required to determine accurately the aeroplane flight path, speed, attitude, engine power, and configuration of lift and drag devices. The operational parameters required to be recorded by digital flight data recorders include longitudinal acceleration, lateral acceleration, pitch trim surface position, trailing/leading edge flap or cockpit flap control selection, each thrust reverser position, ground spoiler position or speed brake selection, outside or total air temperature, automatic flight control system (AFCS) modes and engagement status, including autothrottle, radio altitude, localizer deviation, MLS azimuth, glideslope deviation, MLS elevation, marker beacon passage, master warning, air/ground sensor, angle of attack, hydraulic pressure low, ground speed, ground proximity warning system, landing gear position, drift angle, wind speed and direction, latitude and longitude, stick shaker/pusher, and windshear.

Digital flight data recorders record additional engine parameters like flap position and auto-pilot mode or even smoke alarms. The number of parameters to be recorded depends on aeroplane complexity and MTOW. The flight data acquisition unit collects parameters from analog or digital sources. Digital DFDAU complies with ARINC 717, while analog FDAU are compliant to ARINC 573.

What is a Flight Data Recorder Reader?

A Flight Data Recorder Reader is the laboratory assembly of manufacturer-developed hardware and software that physically connects to a Flight Data Recorder (FDR) and extracts the binary file stored in its crash-survivable memory. The same equipment is used for scheduled maintenance, when a total of 1 hour of recorded data is erased for testing, and for post-accident investigation, when every parameter remains intact. Dallas-based Flight Data Systems offers such a device under the name SAFR Readout, a state-of-the-art secure Flight Data Recorder (FDR) and Cockpit Voice Recorder (CVR) data analysis service that addresses the requirement for aircraft operators to perform periodic maintenance readouts on flight recorder systems at least once a year. During a readout session the reader decodes instructions sent to any electronic systems on an aircraft, converts raw bits into engineering units, and feeds the results to readout analysts who create recognized CASA or EASA readout reports that state the condition of the aircraft's flight recorder system serviceability. Because the memory unit is designed to survive impact and fire, the reader must be able to communicate even when the outer chassis is distorted. Once the survivable memory is recovered, the same manufacturer-developed software used for routine checks is employed to verify that the crash-protected file can still be downloaded without alteration.

Why are Flight Data Recorders kept in water?

When a recorder is lifted from saltwater, investigators immediately slide it into a cooler of fresh, clean water. This bath prevents deposits like salt or minerals from drying out inside the housing. If the casing is breached, corrosion begins immediately in open air and keeping the device immersed delays the onset of corrosion because dissolved oxygen in water is lower than oxygen in air. Immersion therefore safeguards data until technicians can properly clean and dry every section in a laboratory.

Recovered flight recorders remain submerged until they reach the NTSB lab, where technicians take the recorder out of the freshwater bath, rinse away salt, and dry any surfaces that were exposed to water. The same method is employed for both the Flight Data Recorder and the Cockpit Voice Recorder. By preserving the recorder in water from the moment of recovery, investigators guarantee that the crash-survivable memory units can later yield their full narrative of the flight.

What is Flight Data Recorder testing?

Flight Data Recorder (FDR) testing is a planned sequence of ground and flight checks that confirm every installed recorder can capture, encode, erase and survive precisely as regulations demand. Tests must be performed for a newly installed flight recorder system and at intervals thereafter, follow-on installations omit flight testing, although the installer and operator must still retain a copy of the actual ground data and final report. Strict erasure rules apply: a total of 1 hour of recorded data will be erased for the purpose of testing, but any erasure must be of the oldest recorded data accumulated at the time of testing.

Each procedure is split into two phases. Ground tests include sensor calibration that has to be performed for each parameter, after which the flight recorder system test includes a conversion and logic for translation of the recorded data stream into parameters expressed in engineering units. Flight tests reproduce the operational environmental conditions of FDR systems, confirm the results of ground tests, and are recorded in graphical and tabular format, the resulting report shall contain the results of all ground and flight tests, including calibrations and correlations, with a sufficient number of correlation points to accurately establish conversion from recorded values to engineering units over the full operating range of each parameter.

Built-in aids shorten fault isolation. The recorder added power-on, pilot-initiated and continuous built-in-test features that rapidly identify and report fault conditions, while simple inspections, regular testing, and maintenance mean the difference between recovering full, usable data or losing it.

Separate environmental trials guarantee crash survival. The black box is only used if it passes safety tests: high-temperature fire test 1100°C (2012°F) for 30 minutes increased to 60 minutes and low temperature fire test 260°C (500°F) for 10 hours incorporated. A shear and tensile test guarantees the ULB will not be separated from a crash protected memory unit. The sea water immersion test duration is altered from 30 to 90 days.

What are the regulations for Flight Data Recorders?

The regulations for Flight Data Recorders are set by FAR 91.609, FAR 125.226 and FAR 135.152. They apply by the date the Initial Certificate of Airworthiness (or, for foreign-registered imports, the Initial FAA Import Certificate) is issued.

Airplanes with more than 19 seats must carry two separate recorders: one Flight Data Recorder and one Cockpit Voice Recorder. Rotorcraft use one combination unit so long as no single electrical failure disables both functions.

Aircraft manufactured after 18 August 2000 must install each recorder in accordance with 23.1459 or 25.1459, while aircraft built after 7 April 2010 must meet TSO C124a (or later) and retain the last 25 hours of operation. Multi-engine, turbine-powered airplanes with 10-19 seats follow the same 25-hour rule; earlier models built between 1991 and 2010 need only 8 hours.

Every recorder must operate continuously from take-off roll to landing roll, carry an approved underwater-locating device, and be placed in the most crash-survivable part of the aircraft, normally the aft fuselage. A pre-flight aural or visual check is mandatory, and an annual read-out verifies that at least 95 % of the required parameters are recorded.

If an accident terminates the flight and immediate NTSB notification is required under 49 CFR part 830, the certificate holder must remove the recording medium and keep it for at least 60 days, or longer if the Board requests. Calibration data and recorder correlation must be retained for the life of the aircraft.

When was the first Flight Data Recorder made?

The first Flight Data Recorder was made in 1939 by French engineers Fran ois Hussenot and Paul Beaudouin at the Marignane flight test center, France. Their photograph-based device, later called the type HB or hussenograph, used a scrolling photographic film 8 metres (26.2 feet) long by 88 millimetres (3.46 inches) wide to record altitude and speed. This analog, film-based military recorder remained in use until 1970.

The first modern Flight Data Recorder, named Mata-Hari after the famous spy, was created in 1942 by Finnish aviation engineer Veijo Hietala. It marked a new type of recorder developed after WWII.