12.5 Integrated Engine Indicating: EICAS, ECAM, Annunciators & Range Markings
Key Takeaways
- FAA-H-8083-32B defines the instrument marking system in three colors: a red line or mark is a point beyond which a dangerous operating condition exists, a yellow arc is a caution range, and a green arc is the normal and safe operating range.
- A red arc, unlike a red radial line, marks a range that may be passed through but not operated in, and it generally exists because of an engine or propeller vibration range.
- When range markings are applied to the cover glass rather than the dial face, a white radial slippage mark is added; if the white line no longer aligns across the glass and case, the glass has rotated and every other marking on it is mislocated.
- EICAS is a two-monitor, two-computer system with a display select panel; the top monitor carries full-time primary engine parameters such as EPR, N1, and EGT plus advisories and warnings, while the lower screen carries secondary parameters, system status, and on-ground maintenance diagnosis.
- EICAS automatically records the parameters of a failure event for maintenance review, and the crew can press the event record button on the display select panel to capture a suspect flight period.
12.5 Integrated Engine Indicating: EICAS, ECAM, Annunciators & Range Markings
Quick Answer: FAA-H-8083-32B defines engine instrument markings in three colors: "A red line, or mark, indicates a point beyond which a dangerous operating condition exists. A red arc indicates a dangerous operating range due generally to an engine propeller vibration range. This arc can be passed through, but the engine cannot be operated in this area." The yellow arc is a caution range on the outer circumference, the green arc is the normal and safe range of operation, and when markings are applied to the cover glass "a white line is used as an index mark, often called a slippage mark." On transport aircraft those markings are replaced by an integrated display: EICAS "performs many of the same functions as an ECAM system" and is "a two-monitor, two-computer system with a display select panel" that presents "full time primary engine parameters (EPR, N1, EGT) on the top, primary monitor" with "secondary engine parameters and nonengine system status... displayed on the bottom screen."
Why This Section Exists
The Powerplant ACS instrument-systems subject lists eleven knowledge elements. Sections 12.1 through 12.4 covered the sensing and transmission of pressure, temperature, speed, EPR, and fuel flow. This section covers the four that are about how the information is presented and bounded: annunciator indicating systems, EICAS, ECAM, and engine instrument range markings and instrument conditions. A technician who can troubleshoot a thermocouple harness but cannot say what a red arc means, or which EICAS screen a secondary parameter lives on, has a real gap.
Part 1: Range Markings on Conventional Instruments
The Three Colors and the Fourth Mark
"Instrument markings, ranges of operation, minimum and maximum limits, and the interpretation of these markings are general to all the instruments. Generally, the instrument marking system consists of three colors: red, yellow, and green."
| Marking | Meaning | Where it appears |
|---|---|---|
| Red radial line | "A point beyond which a dangerous operating condition exists." | Located radially on the cover glass or dial face; the handbook notes the red mark "is used more commonly" than the red arc |
| Red arc | "A dangerous operating range due generally to an engine propeller vibration range. This arc can be passed through, but the engine cannot be operated in this area." | Typically on a tachometer, marking a restricted rpm band |
| Yellow arc | "Covers a given range of operation and is an indication of caution." | "Generally... located on the outer circumference of the instrument cover glass or dial face" |
| Green arc | "Shows a normal and safe range of operation." | Dial face or cover glass |
| White radial slippage mark | "When the markings appear on the cover glass, a white line is used as an index mark, often called a slippage mark. The white radial mark indicates any movement between the cover glass and the case, a condition that would cause mislocation of the other range and limit markings." | Split across the glass-to-case joint |
Two distinctions carry most of the exam weight:
Red line versus red arc. A red radial line is a limit — a boundary you do not cross. A red arc is a band — you may transit it but you may not operate within it. The physical reason for a red arc is almost always a resonant vibration range of the engine-propeller combination, which is exactly the torsional and blade-excitation phenomenon Sections 2.2 and 7.2 cover. Sitting in that band builds fatigue damage; passing quickly through it does not.
Why the white slippage mark matters more than it looks. If range markings are painted on the dial face, they cannot move relative to the pointer. If they are painted on the cover glass, the entire set of markings depends on the glass staying clocked to the case. The white radial line is drawn across that joint so that any rotation shows up as a break in the line. A broken slippage mark does not mean the instrument is inaccurate; it means every colored marking on the glass is now in the wrong place, so the instrument must be removed and re-marked or replaced before the indications can be trusted.
Reading the Limits Off the Right Document
The handbook is explicit that the numbers themselves come from the aircraft data, not from the gauge: "The oil pressure gauge dial does not show the pressure range or limits for all installations. The actual markings for specific aircraft may be found in the aircraft specifications or Type Certificate Data Sheets." Its worked example for one installation is a lower red line at 25 psi for minimum oil pressure permissible in flight, a green arc between 60 and 85 psi for the desired operating range, and a red line at 100 psi for maximum permissible oil pressure.
The same pattern appears on the other engine instruments. On the oil temperature gauge the handbook describes three range markings, with a green range for continuous operation and a red mark at the maximum permissible oil temperature. On a manifold pressure gauge it describes a green arc running through the normal operating band with a red line at the maximum permissible manifold pressure. On a tachometer the green arc indicates the rpm range within operation that is permissible and the red line indicates maximum rpm.
The verification task. When an instrument is replaced or re-marked, the markings must be verified against the aircraft specification or TCDS for that installation, not copied from another aircraft of the same model. Two aircraft of one model with different engines or different propellers can carry different red arcs.
Part 2: Annunciator Indicating Systems
The ACS lists annunciator indicating systems (warning, caution, and advisory lights) as its own knowledge element because an annunciator is not simply a lamp — it is a prioritized message.
The convention that runs through transport and modern general aviation flight decks:
| Level | Colour | Crew expectation |
|---|---|---|
| Warning | Red | Immediate action required; usually accompanied by an aural tone |
| Caution | Amber / yellow | Immediate crew awareness, subsequent action required |
| Advisory | Green, white, or blue | Status information; no action required |
FAA-H-8083-32B describes exactly this integration in the EICAS context: "Caution and warning lights, as well as aural tones, are incorporated," and "color coding is used, as well as message prioritizing."
The press-to-test function is the item most often tested on the maintenance side. Every annunciator panel provides a lamp test that proves the bulb or LED and its drive circuit. Section 16.1 covers the equivalent function on a fire-detection system, where the press-to-test both proves the lamp and, on most designs, proves loop continuity. The general rule for the technician: a lamp that fails press-to-test is a dispatch item in its own right, because a dark annunciator and a healthy system look identical from the flight deck.
Part 3: EICAS and ECAM
What They Replace
On a conventional flight deck each engine parameter has its own round gauge with its own markings. On a transport aircraft that becomes dozens of instruments for two to four engines, plus separate panels for the airframe systems. EICAS (Engine Indicating and Crew Alerting System, the Boeing term) and ECAM (Electronic Centralized Aircraft Monitor, the Airbus term) collapse all of it onto two screens with computer-managed prioritization.
"An engine indicating and crew alerting system (EICAS) performs many of the same functions as an ECAM system. The objective is still to monitor the aircraft systems for the pilot. All EICAS display engine, as well as airframe, parameters. Traditional gauges are not utilized, other than a standby combination engine gauge in case of total system failure."
That last clause is the one candidates forget: there is still a standby combination engine gauge, precisely because the electronic system can fail completely.
Architecture
"EICAS is also a two-monitor, two-computer system with a display select panel. Both monitors receive information from the same computer. The second computer serves as a standby. Digital and analog inputs from the engine and airframe systems are continuously monitored."
| Element | Function |
|---|---|
| Upper (primary) monitor | "Full time primary engine parameters (EPR, N1, EGT)" plus "advisories and warnings" |
| Lower monitor | "Secondary engine parameters and nonengine system status"; also "used for maintenance diagnosis when the aircraft is on the ground" |
| Two computers | One active, "the second computer serves as a standby" |
| Display select panel | "Allows the pilot to choose which computer is actively supplying information. It also controls the display of secondary engine information and system status displays on the lower monitor." |
| Standby engine gauge | Conventional combination instrument retained "in case of total system failure" |
The Maintenance Feature That Matters Most
"EICAS has a unique feature that automatically records the parameters of a failure event to be regarded afterwards by maintenance personnel. Pilots that suspect a problem may be occurring during flight can press the event record button on the display select panel. This also records the parameters for that flight period to be studied" later.
For a powerplant technician this changes the troubleshooting workflow entirely. On a conventional aircraft an intermittent engine indication produces a squawk describing what the crew remembers seeing. On an EICAS aircraft, the recorded event is the primary evidence, and the lower display in ground mode is the readout device. The first step on receiving an engine squawk is to retrieve the event record, not to start swapping line-replaceable units.
How This Connects to the Rest of the Chapter
The parameters EICAS presents are the ones the preceding sections produce:
- EPR comes from the Pt2 and Pt7/Pt5 total-pressure probes of Section 12.4 — including the Pt2 icing failure mode that produces a false high EPR.
- N1 and N2 come from the phonic-wheel and variable-reluctance pickups of Section 12.3.
- EGT and ITT come from the averaged thermocouple harnesses of Section 12.2.
- Oil and fuel pressure come from the transducers of Section 12.1.
- FADEC status and engine control faults annunciate here; Section 13.3 covers the dual-channel EEC that generates them.
The digital display does not change the sensor's failure modes. A drifting thermocouple, a chafed harness, or a blocked Pt2 probe produces exactly the same wrong number whether it is drawn as a needle or as a digital readout — and the electronic display can make the error more convincing because it renders a precise figure. The troubleshooting still starts at the probe.
Independent Prep Note
Independent FAA AMT Powerplant prep by OpenExamPrep. Not sponsored by or affiliated with the Federal Aviation Administration (FAA). Technical data compiled from FAA-H-8083-32B, FAA AC 43.13-1B, and 14 CFR Parts 43 and 65.
An engine tachometer carries a red arc between 2,100 and 2,350 rpm in addition to a red radial line at 2,700 rpm. What is the operational difference between the two markings?
During an inspection, a technician finds that the white radial line on an oil pressure gauge no longer lines up across the joint between the cover glass and the instrument case. What does this indicate?
On an EICAS-equipped aircraft, which parameters appear full time on the upper primary monitor, and what is the lower monitor used for on the ground?
A flight crew reports an intermittent engine indication that did not repeat on the ground. On an EICAS-equipped aircraft, what is the technician's most productive first step?