14 CFR Part 135eCFR Sep 29, 2026
Appendix E to Part 135
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.