Engine temperature constraints are behind a series of special conditions that the US Federal Aviation Administration (FAA) levied on Embraer as a condition for receiving Phenom 300 business jet certification in the US. The Brazilian airframer certified the six-passenger Pratt & Whitney Canada PW535E-powered twinjet in Brazil on 3 December, followed by FAA certification on 14 December.
The FAA went above and beyond Brazilian authorities in the area of ice protection at altitude however, requiring Embraer to address a built-in inhibit for wing and horizontal stabilizer leading edge bleed-air anti-icing protection when the aircraft is flying above 30,000ft (9,144m) or when the air temperature is above a certain temperature. The agency cites a technical report (ADS-4) as including three reported icing encounters above 30,000ft, including a severe icing encounter at 37,00ft and a light icing encounter at 39,000ft.
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“Due to potential over-temperature of the engines, the ice protection system is designed to inhibit (above 30,000ft)…even if there are ice accretions the airframe,” the FAA states in the special conditions, published today. In the cockpit, if the pilot selects the “WINGSTAB” switch to “ON” where the inhibits are active, the airframe anti-ice valves will remain off and a caution message, ‘A-I WINGSTB OFF’, is displayed on the cockpit alerting system, “making the pilot aware that the wing and horizontal stabilizer anti-ice system is not operational”, says the FAA.
Of the two choices offered – prohibiting flight in icing conditions above 30,000ft or having no restrictions above 30,000ft through a series of suggested flight tests – the FAA notes that Embraer had proposed to prohibit flight in those conditions, with pilots instructed to exit icing conditions.
Embraer confirms that it addressed the FAA's special conditions by including aircraft flight manual (AFM) instructions for leaving icing conditions when encountered above 30,000ft. The airframer notes that FAA certification rules define tests for continuous icing through 22,000ft and intermittent icing only up to 30,000ft. "Because of the very low frequency of finding such conditions (icing above 30,000ft), the required AFM procedure does not represent a practical restriction to the aircraft," Embraer tells Flight International.
"Aircraft anti-ice systems are designed to comply with these conditions and the Phenom 300 is not different in that regards," Embraer continues. "The reason for the FAA issue paper for the Phenom 300 is the fact that portion of the anti-ice system is inhibited when flying outside the appendix C (icing requiremenets)envelope."
Included in FAA's new requirements is that "icing cues must be substantiated or an ice detector installed", along with an aircraft flight manual limitation prohibiting such operations and a cockpit placard. Also the aircraft’s stall warning system must provide the same margin for recovery as for non-icing conditions. “This is shown by showing stalling or large roll excursion can be avoided if the pilot delays recovery for one second after stall warning in a one-knot-per-second deceleration, wings level and turning flight,” the special conditions note.
Embraer notes that it "went a step further and flight tested the airplane in those conditions, demonstrating its capability to safely leave such icing encounters".
The FAA also required that Embraer not inhibit engine inlet anti-icing protection “since loss of thrust from both engines is classified as a hazard” for the Phenom 300 class of aircraft.
Source: FlightGlobal.com
