14 CFR · Part 135
14 CFR Part 135, Appendix E
Helicopter Flight Recorder Specifications
| Parameters | Range | Accuracy sensor input to DFDR readout | Sampling interval (per second) | Resolution ² read out |
|---|---|---|---|---|
| Time (GMT) | 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 30′. |
| Airspeed | As the installed measuring system | ±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° | 2 | 0.5° |
| Roll Attitude | ±180° | ±2° | 2 | 0.5°. |
| Radio Transmitter Keying | On-Off (Discrete) | 1 | 0.25 sec | |
| Power in Each Engine: Free Power Turbine Speed and Engine Torque | 0-130% (power Turbine Speed) Full range (Torque) | ±2% | 1 speed 1 torque (per engine) | 0.2% ¹ to 0.4% ¹ |
| Main Rotor Speed | 0-130% | ±2% | 2 | 0.3% ¹ |
| Altitude Rate | ±6,000 ft/min | As installed | 2 | 0.2% ¹ |
| Pilot Input—Primary Controls (Collective, Longitudinal Cyclic, Lateral Cyclic, Pedal) ³ | Full range | ±3% | 2 | 0.5% ¹ |
| Flight Control Hydraulic Pressure Low | Discrete, each circuit | 1 | ||
| Flight Control Hydraulic Pressure Selector Switch Position, 1st and 2nd stage | Discrete | 1 | ||
| AFCS Mode and Engagement Status | Discrete (5 bits necessary) | 1 | ||
| Stability Augmentation System Engage | Discrete | 1 | ||
| SAS Fault Status | Discrete | 0.25 | ||
| Main Gearbox Temperature Low | As installed | As installed | 0.25 | 0.5% ¹ |
| Main Gearbox Temperature High | As installed | As installed | 0.5 | 0.5% ¹ |
| Controllable Stabilator Position | Full Range | ±3% | 2 | 0.4% ¹. |
| Longitudinal Acceleration | ±1g | ±1.5% max range excluding datum error of ±5% | 4 | 0.01g. |
| Lateral Acceleration | ±1g | ±1.5% max range excluding datum of ±5% | 4 | 0.01g. |
| Master Warning | Discrete | 1 | ||
| Nav 1 and 2 Frequency Selection | Full range | As installed | 0.25 | |
| Outside Air Temperature | −50 °C to + 90 °C | ±2° c | 0.5 | 0.3° c |
¹ Per cent of full range. ² This column applies to aircraft manufactured after October 11, 1991. ³ For all aircraft manufactured on or after December 6, 2010, the sampling interval per second is 4.
Reflects the eCFR edition current as of September 29, 2026. Retrieved from ecfr.gov on October 16, 2026.
Primary Source