Consultation expired with comments. The proposed Special Condition (SC) has been editorially updated based on the comments received, and the corresponding Comment-Response Document (CRD) has been completed by EASA.
Details
Identification of issue
EASA received an application for a major design change on a CS 25 twin turboprop powered aircraft. The proposed design change incorporates a single lever per engine dedicated to power control, with full automation of the propeller speed and pitch controls. It is considered that the applicable CS 25.1149 “Propeller speed and pitch controls” at amendment level 27 does not contain adequate or appropriate safety standards for such “novel or unusual design features” of the throttle quadrant.
The CS 25.1149 “Propeller speed and pitch controls” states:
- There must be a separate propeller speed and pitch control for each propeller.
- The controls must be grouped and arranged to allow –
- Separate control of each propeller; and
- Simultaneous control of all propellers.
- The controls must allow synchronisation of all propellers.
- The propeller speed and pitch controls must be to the right of, and at least 25 mm (one inch) below, the pilot’s throttle controls.
The paragraph CS 25.1149 is harmonized with FAA’s paragraph 25.1149 of 14 CFR Part 25 Initial Issue, which itself is derived from the older paragraph 4b.474 of CAR 4b. The intent of this paragraph was to provide requirements for propeller speed and pitch control in the context of early generation transport airplanes powered by piston or turboprop engines.
Due to the progress of electronics, the modern cockpit designs generally intend to maximize automation to reduce flight crew workload. In this context, some applicants have proposed throttle quadrant layout featuring a single lever per engine dedicated to power control, with full automation of the propeller speed and pitch control.
Such throttle quadrant layout cannot be demonstrated as compliant with the paragraph 25.1149, which have led the Agency to accept Equivalent Safety Findings in the past.
It is acknowledged that the current provisions of CS 25.1149 are outdated for recent and future throttle quadrant design for turboprop powered aeroplanes. This may lead the applicants to propose partially compliant, “in-between” designs which may not take full credit of the available technologies and reduce their safety benefit.
This Special Condition intends to provide new requirements for propeller speed and pitch control.
