14 CFR Part 121eCFR Sep 29, 2026
Appendix B to Part 121
Airplane Flight Recorder Specification
| Parameters | Range | Accuracy sensor input to DFDR readout | Sampling interval (per second) | Resolution ⁴ readout |
|---|---|---|---|---|
| Time (GMT or Frame Counter) (range 0 to 4095, sampled 1 per frame) | 24 Hrs | ±0.125% Per Hour | 0.25 (1 per 4 seconds) | 1 sec. |
| Altitude | −1,000 ft to max certificated altitude of aircraft | ±100 to ±700 ft (See Table 1, TSO-C51a) | 1 | 5′ to 35′ ¹ |
| Airspeed | 50 KIAS to V so, and V so to 1.2VD | ±5%, ±3% | 1 | 1 kt. |
| Heading | 360° | ±2° | 1 | 0.5° |
| Normal Acceleration (Vertical) | −3g to + 6g | ±1% of max range excluding datum error of ±5% | 8 | 0.01g. |
| Pitch Attitude | ±75° | ±2° | 1 | 0.5° |
| Roll Attitude | ±180° | ±2° | 1 | 0.5° |
| Radio Transmitter Keying | On-Off (Discrete) | ±2° | ±2% | |
| Thrust/Power on Each Engine | Full Range Forward | ±2° | 1 (per engine) | 0.2% ² |
| Trailing Edge Flap or Cockpit Control Selection | Full Range or Each Discrete Position | ±3° or as Pilot's Indicator | 0.5 | 0.5% ² |
| Leading Edge Flap or Cockpit Control Selection | Full Range or Each Discrete Position | ±3° or as Pilot's Indicator | 0.5 | 0.5% ² |
| Thrust Reverser Position | Stowed, In Transit, and Reverse (Discrete) | 1 (per 4 seconds per engine) | ||
| Ground Spoiler Position/Speed Brake Selection | Full Range or Each Discrete Position | ±2% Unless Higher Accuracy Uniquely Required | 1 | 0.2% ². |
| Marker Beacon Passage | Discrete | 1 | ||
| Autopilot Engagement | Discrete | 1 | ||
| Longitudinal Acceleration | ±1g | ±1.5% max range excluding datum error of ±5% | 4 | 0.01g. |
| Pilot Input and/or Surface Position—Primary Controls (Pitch, Roll, Yaw) ³ | Full Range | ±2° Unless Higher Accuracy Uniquely Required | 1 | 0.2% ². |
| Lateral Acceleration | ±1g | ±1.5% max range excluding datum error of ±5% | 4 | 0.01g. |
| Pitch Trim Position | Full Range | ±3% Unless Higher Accuracy Uniquely Required | 1 | 0.3% ². |
| Glideslope Deviation | ±400 Microamps | ±3% | 1 | 0.3% ². |
| Localizer Deviation | ±400 Microamps | ±3% | 1 | 0.3% ². |
| AFCS Mode and Engagement Status | Discrete | 1 | ||
| Radio Altitude | −20 ft to 2,500 ft | ±2 Ft or ±3% Whichever is Greater Below 500 Ft and ±5% Above 500 Ft | 1 | 1 ft + 5% ² above 500′. |
| Master Warning | Discrete | 1 | ||
| Main Gear Squat Switch Status | Discrete | 1 | ||
| Angle of Attack (if recorded directly). | As installed | As installed | 2 | 0.3% ² |
| Outside Air Temperature or Total Air Temperature. | −50 °C to + 90 °C | ±2 °c | 0.5 | 0.3 °c |
| Hydraulics, Each System Low Pressure | Discrete | 0.5 | or 0.5% ² | |
| Groundspeed. | As installed | Most Accurate Systems Installed (IMS Equipped Aircraft Only) | 1 | 0.2% ² |
| If additional recording capacity is available, recording of the following parameters is recommended. The parameters are listed in order of significance: | ||||
| Drift Angle | When available, As installed | As installed | 4 | |
| Wind Speed and Direction | When available, As installed | As installed | 4 | |
| Latitude and Longitude | When available, As installed | As installed | 4 | |
| Brake pressure/Brake pedal position | As installed | As installed | 1 | |
| Additional engine parameters: | ||||
| EPR | As installed | As installed | 1 (per engine). | |
| N1 | As installed | As installed | 1 (per engine). | |
| N2 | As installed | As installed | 1 (per engine). | |
| EGT | As installed | As installed | 1 (per engine). | |
| Throttle Lever Position | As installed | As installed | 1 (per engine). | |
| Fuel Flow | As installed | As installed | 1 (per engine). | |
| TCAS: | ||||
| TA | As installed | As installed | 1 | |
| RA | As installed | As installed | 1 | |
| Sensitivity level (as selected by crew) | As installed | As installed | 2 | |
| GPWS (ground proximity warning system) | Discrete | 1 | ||
| Landing gear or gear selector position | Discrete | 0.25 (1 per 4 seconds) | ||
| DME 1 and 2 Distance | 0-200 NM; | As installed | 0.25 | 1 mi. |
| Nav 1 and 2 Frequency Selection | Full range | As installed | 0.25 | |
¹ When altitude rate is recorded. Altitude rate must have sufficient resolution and sampling to permit the derivation of altitude to 5 feet. ² Per cent of full range. ³ For airplanes that can demonstrate the capability of deriving either the control input on control movement (one from the other) for all modes of operation and flight regimes, the “or” applies. For airplanes with non-mechanical control systems (fly-by-wire) the “and” applies. In airplanes with split surfaces, suitable combination of inputs is acceptable in lieu of recording each surface separately. ⁴ This column applies to aircraft manufactured after October 11, 1991.