Regulation · 14 CFRCurrent as of October 29, 2026 (eCFR)
14 CFR Part 135 App. E Helicopter Flight Recorder Specifications
Subpart L—Helicopter Air Ambulance Equipment, Operations, and Training Requirements
A reference copy of the official regulation text for study. It is not legal advice or an FAA interpretation; always confirm against the current official source.
| 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.
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