Appendix 2 – Powerplant Displays

ED Decision 2011/004/R

1.       General

At the time CS 25.1305 was adopted, flight deck powerplant displays were primarily a collection of dedicated, independent, full-time analogue “round dial” type instruments. Typically, there was one display for each required indication. Today, flight deck powerplant displays are primarily electronic displays integrated with other flight deck displays on a few relatively large electronic display spaces. Throughout this technological evolution, the Agency has used certification review items (CRIs) to assure that this new technology, with its increased potential for common faults and the challenges of effectively sharing display space, did not adversely impact the timely availability and independence of the powerplant information required to meet the intent of CS 25.1305. This AMC provides some of that guidance material.

To comply with one of the provisions of CS 25.1305, a display should provide all the instrument functionality of a full-time, dedicated analogue type instrument as intended when the specification was adopted (see AC 20-88A, Guidelines on the Marking of Aircraft). The design flexibility and conditional adaptability of modern displays were not envisioned when CS 25.1305 and CS 25.1549 were initially adopted. In addition, the capabilities of modern control systems to automate and complement flight crew functions were not envisioned. In some cases these system capabilities obviate the need for a dedicated full-time analogue type instrument.

When making a compliance finding, all uses of the affected displays should be taken into consideration, including:

(1)     Flight deck indications to support the approved operating procedures (CS 25.1585),

(2)     Indications as required by the powerplant system safety assessments (CS 25.1309), and

(3)     Indications required in support of the instructions for continued airworthiness 25.1529).

For example:

Compliance with CS 25.1305(c)(3) for the engine N2 rotor was originally achieved by means of a dedicated, full time analogue instrument. This provided the continuous monitoring capability required to:

—          Support engine starting (for example, typically used to identify fuel on point);

—          Support power setting (for example, sometimes used as primary or back up parameter);

—          “Give reasonable assurance that those engine operating limitations that adversely affect turbine rotor structural integrity will not be exceeded in service” as required by CS 25.903(d)(2);

—          Provide the indication of normal, precautionary, and limit operating values required by CS 25.1549; as well as

—          Support detection of unacceptable deterioration in the margin to operating limits and other abnormal engine operating conditions as required to comply with CS 25.901, CS 25.1309, etc.

As technology evolved full authority digital engine controls (FADECs) were introduced. The FADECs were designed with the ability to monitor and control engine N2 rotor speed as required to comply with CS 25.903(d)(2). Additionally, engine condition monitoring programmes were introduced and used to detect unacceptable engine deterioration. Flight deck technology evolved such that indications could be displayed automatically to cover abnormal engine operating conditions. The combination of these developments obviated the need for a full time analogue N2 rotor speed indication, in accordance with the guidance found in Chapter 6, paragraph 36c(3) of this AMC.

2.      Design Guidelines

Safety-related engine limit exceedances should be indicated in a clear and unambiguous manner. Flight crew alerting is addressed in CS 25.1322.

If an indication of significant thrust loss is provided it should be presented in a clear and unambiguous manner.

In addition to the failure conditions listed in Chapter 4 of this AMC, the following design guidelines should be considered:

1.       For single failures leading to the non-recoverable loss of any indications on an engine, sufficient indications should remain to allow continued safe operation of the engine. (See CS 25.901(b)(2), CS 25.901(c), and CS 25.903(d)(2)).

2.       No single failure could prevent the continued safe operation of more than one engine or require immediate action by any flight crew member for continued safe operation. (See CS 25.901(c), CS 25.903(b), and CS 25.1309(b)).

3.       Engine indications needed during engine re-start should be readily available after an engine out event. (See CS 25.901(b)(2), CS 25.901(c), CS 25.903(d)(2), CS 25.903(e), CS 25.1301, CS 25.1305, CS 25.1309, and Chapter 6, paragraph 36c(3) of this AMC).

[Amdt 25/11]