The vocabulary of the trade, in a few sentences.

A plug-in board dedicated to one signal family: analog, strain gauge, thermocouple, IEPE, MIL-STD-1553, ARINC 429, PCM, video… Modules stack in a unit and are ordered by channel count, which is why a D.T.MUX reference lists them one by one.

The false frequency that appears when a signal is sampled too slowly: a 900 Hz vibration sampled at 1 000 Hz shows up as a 100 Hz component that never existed. Prevented by an anti-aliasing filter ahead of the converter and a sample rate well above twice the highest frequency of interest.

The point-to-point avionics data bus of civil aircraft: one transmitter, up to twenty receivers, 32-bit words at 12.5 or 100 kbit/s, each word identified by a label. An acquisition module records the words with their time; the meaning of each label comes from the aircraft documentation.

The serial frame that feeds a civil flight data recorder: 64 to 1 024 twelve-bit words per second, organised in four one-second subframes. Recording it as received keeps the recorder faithful to what the aircraft actually sent; decoding it needs the aircraft data frame document.

A recorder whose memory survives an accident: fire, impact, static crush, penetration, deep-sea immersion, each tested at the levels of ED-112A or ED-155. Everything else about the unit may be destroyed; the data must be recoverable. It is not the same thing as a rugged recorder.

Crash-Survivable Memory Unit: the armoured core of a crash-protected recorder, a memory module wrapped in thermal insulation and a steel or titanium shell. Only the CSMU has to survive the accident; the electronics around it does the recording in normal life.

Cockpit Voice Recorder: the crash-protected recorder of cockpit audio, microphones and radio channels, in a loop of the last two hours or more. On modern combined units the same CSMU also holds flight data and, increasingly, cockpit video.

ETEP's native recording format, born when the medium was still tape (Data Tape Multiplexed): all channels interleaved on one time base with a descriptive header, the secretariat. It is what the D.T.MUX Viewer replays, and it converts losslessly to Chapter 10.

The box that turns physical signals into time-stamped digital data: it conditions the sensors, samples them, reads the avionics buses and hands everything to a recorder or a telemetry link on a single time base. In the D.T.MUX range the unit is modular, one acquisition module per signal family.

Taking a PCM frame apart to recover the individual parameters: finding the synchronisation word, counting the words, and mapping each position to a measurement with its scaling. The ground station does it in real time; replay software does it after the flight.

The environmental qualification standard for airborne equipment: temperature, altitude, humidity, vibration, shock, fluids, sand, icing, lightning, EMC… Each section defines categories; a product declares which category it demonstrated, section by section. ETEP applies edition G.

The EUROCAE minimum operational performance specification for crash-protected airborne recorders: what a flight data, cockpit voice, data-link or image recorder must record, how long, and what it must survive. The reference for certified aircraft in Europe.

The EUROCAE specification for lightweight flight recording systems, written for aircraft where a full ED-112A recorder does not fit: helicopters, light aircraft, some drones. Reduced survivability levels, a smaller and lighter unit, the same idea.

Electromagnetic compatibility: the equipment must neither disturb its neighbours (emissions) nor be disturbed by them (immunity), conducted and radiated. Tested in an anechoic chamber against DO-160 sections 20 and 21 or MIL-STD-461.

Flight Data Recorder: the crash-protected recorder of the mandatory flight parameters, altitude, speed, heading, attitude, engine data, control positions, over the last 25 hours. Its content is fixed by regulation; a flight-test recorder records what the test needs, which is a different job.

The temporary measurement chain fitted to an aircraft under test: sensors, acquisition units, recorders, a telemetry transmitter and the ground station that receives it. It must be installed without altering the aircraft it measures, and removed once the campaign ends.

The absolute time delivered by a GPS receiver, accurate to well under a microsecond once the pulse-per-second output is used. Recorders take it to stamp their data; the ground station uses it to align what it receives with what was recorded on board.

An accelerometer or microphone with built-in electronics, powered through its own signal cable by a constant current. The acquisition module supplies the current and reads the voltage; no separate power line, which is why IEPE dominates vibration measurement.

The open recording format of the flight-test community: a packet structure where every channel, analog, bus, video or PCM, is time-stamped and described in a header. A Chapter 10 file can be replayed by any compliant software, which is why it is the exchange format of choice between test centres.

The part of IRIG 106 that standardises PCM telemetry frames: word length, frame and subframe structure, synchronisation patterns. A transmitter and a ground station that both follow Chapter 4 can be paired without a custom decoder.

The classic time code of test ranges: one frame per second carrying the time of day, as a modulated analog signal or a DC level shift. Still the simplest way to give several recorders and a ground station exactly the same clock.

The account of every gain and loss between the airborne transmitter and the ground antenna: transmit power, antenna gains, distance, frequency, margins for fading and aircraft attitude. It decides the achievable bit rate and the range at which telemetry stays clean.

The dual-redundant command/response data bus of military avionics: a bus controller polls remote terminals at 1 Mbit/s, every exchange framed by command and status words. A bus monitor records the traffic without taking part in it, which is how a recorder listens.

The environmental test methods of defence equipment: temperature, humidity, altitude, vibration, shock, sand and dust, each described as a procedure to tailor to the platform. Where DO-160 gives categories, MIL-STD-810 gives methods; many programmes ask for both.

Mean Time Between Failures, the predicted reliability of an equipment, computed from the failure rates of its components under a given environment. A figure to compare designs and size spares, not a guarantee for any single unit.

Cameras recorded alongside the data, compressed in H.264 to fit the storage and the telemetry link, and time-stamped so that a frame can be matched to the measurements of the same instant. Bandwidth, latency and synchronisation are the three things to size.

Pulse Code Modulation: the serial stream that carries telemetry, a fixed sequence of words repeated frame after frame, each parameter at its own position and rate. Simple, robust, decodable in real time, and standardised by IRIG 106 Chapter 4.

The option that renders a cartridge memory unusable by damaging the chips themselves, beyond any erase. On D.T.MUX cartridges it is the PD field of the reference; a cartridge without PD has no such function, whatever else it carries.

Precision Time Protocol: time distribution over Ethernet, a grandmaster clock synchronising every device on the network to within a microsecond or better with hardware time-stamping. The natural choice once the instrumentation chain is itself an Ethernet network.

Turning a continuous voltage into one of a finite number of levels: 16 bits give 65 536 steps over the full scale. The step is the smallest change the recording can show; choosing the full scale too wide wastes bits, too narrow clips the signal.

A command that makes the content of a cartridge unrecoverable within seconds, typically by destroying the encryption key rather than overwriting every cell. The QE field of a D.T.MUX cartridge reference.

How many times per second a channel is measured. It fixes the highest frequency the recording can contain, a little under half the rate in practice, and, multiplied by the word length and the channel count, the data rate the recorder and the telemetry link must carry.

A cartridge that encrypts everything it stores with AES 256-bit hardware, transparently for the recorder. Without the key the memory reads as noise; destroying the key is what makes quick erase quick. The DE field of a D.T.MUX cartridge reference.

Everything between the sensor and the converter: excitation, bridge completion for gauges, cold-junction compensation for thermocouples, constant current for IEPE, gain and filtering. Done badly it is the first source of a false measurement; done in the acquisition module it is documented and repeatable.

The spectrally efficient modulation of modern telemetry (ARTM Tier 1): about twice the bit rate of the old PCM/FM in the same bandwidth, with a constant envelope that suits airborne power amplifiers. Often paired with LDPC forward error correction.

The removable solid-state memory of a D.T.MUX recorder: the data leaves the aircraft in the cartridge and is read on the ground with a reader or the Viewer. Capacity and the DE, QE, PD and CP options are all written in its reference.

A resistive sensor bonded to a structure whose resistance changes with its elongation, by a few parts per thousand at most. Read in a Wheatstone bridge with a stable excitation, it gives structural loads and, through calibration, forces and torques.

Sending the measurements to the ground while the test is flying, so that the engineers see them live and can abort or continue. Recording on board remains the reference copy; telemetry is what makes the flight safe and short.

The receiving end of a telemetry link: antenna, receiver, demodulator, bit synchroniser, decommutator, then recording, real-time display and archiving. Everything the airborne side sent has to be usable within seconds by the test engineers.

Two dissimilar metal wires joined at the measuring point, producing a few microvolts per degree between the junction and the connector. Cheap, rugged, good to over 1 000 °C, but it needs cold-junction compensation and careful wiring to be worth trusting.

Giving every element of the chain the same clock, so that a vibration, a bus message and a video frame recorded by different units can be laid side by side after the flight. Achieved with GPS, IRIG-B or PTP; lost, it turns a good recording into a puzzle.

Telemetry Attributes Transfer Standard, IRIG 106 Chapter 9: the text file that describes a recording or a telemetry stream, channels, rates, scalings, data frame. Without it a Chapter 10 file is a sequence of numbers; with it, any software can make sense of them.

The acoustic pinger fixed to a crash-protected recorder, triggered by immersion, emitting at 37.5 kHz for at least 30 days, 90 on recent units, so that the recorder can be found on the sea floor.