As series production of Antonov’s new-generation An-148 and An-158 regional jets gains momentum, the manufacturer and its close ally lessor Ilyushin Finance Co. (IFC) are trying to raise the type’s temporary operational limitations.
The An-158 launch operator, Cubana de Aviación, has already taken three airplanes in a high-density layout with 97 seats at 30-inch pitch and expects to acquire three more this year. The An-158s are powered by D-436 three-shaft turbofans developed by Ivchenko-Progress and manufactured by Motor-Sich. The airline has already flown domestic services and international flights to the Bahamas and the Dominican Republic, and now wants to add more connections–to Venezuela, Ecuador, Costa Rica, Mexico, Honduras, Nicaragua, Panama and Trinidad and Tobago. Some of the destination airports in Latin America are located in the mountains, prompting the carrier to ask the aircraft supplier for hot-and-high capabilities.
Hot-and-high performance is also important for North Korea–already an An-148 operator–and Iran, which signed for 20 aircraft. India, China, Australia and some Latin American and Arab countries, which IFC considers “natural markets” for the Antonov jetliner family, may show more interest in the type should it prove capable of taking passengers into and out of airports located high above sea level.
Ecuador’s Cotopaxi Airport in Latacunga, with an elevation above sea level of 2,806 meters (9,260 feet) was selected for testing, which took place last November 8 to 14. It involved the third deliverable An-158, which was handed over to Cubana two months ago. For the duration of flight tests this airframe was outfitted with special test equipment for accurate measurements and data recording. Ambient air temperature at Latacunga fluctuated between +11 and +21-degrees C, so the deviation from the international standard atmosphere (ISA) varied between +8 and +18 degrees.
After 28 successful engine starts and thorough checking of all on-board systems, the decision was made to proceed to another airport set in a more demanding environment. IFC technical director Yuri Ostrovsky explained: “At this point we decided not to continue with our trials at Latacunga further than ground tests. Instead, we would rather go to La Paz. This way of conducting trials had been prior-agreed with the Cubans.” Consequently, the An-158 flew over to El Alto International Airport (Aeropuerto Internacional El Alto) servicing the capital city of Bolivia. It has elevation above mean sea level of 4,058 meters (13,393 feet). Further complicating the matter, the ambient air temperature at El Alto in the period November 15 to 22 varied between +10 and +18-degrees C. Adjusted to the ISA, the readings rise to almost the maximum temperatures in which the aircraft can operate according to specification (ISA+30).
Starting D-436 engines proved an easy job in all 52 cases, with poor and rich settings of the fuel mixture and use of various starter models. With the cycles done at Latacunga, the grand total came to 80. Hot and cold engines were started. According to Ostrovsky, in all cases the actual readings of gas temperature peaks and time period (to start the engine) appeared a bit below the respective “red-line” figures in the aircraft flight manual. Having assessed the data obtained from these trials, the manufacturer issued a notification to type operators that in the conditions similar to those observed at La Paz, the D-436 engines, after being switched off, need to cool down to 110 to 120 degrees-C in order to get sufficiently cool for reliable starting.
Out of La Paz, Antonov test pilots Sergei Troshin and Andrei Gorin, accompanied by Igor Chernov from Russia’s State Scientific-Research Institute of Civil Aviation (GosNII GA) performed five test flights with several passes over the runway on each mission. Field performance was assessed in various aircraft configurations (clean, flaps down, flaps fully down). Real-life assessment was given to various possible cases, including partial loss of thrust in a simulated engine failure.
Takeoff performance of the aircraft was thoroughly assessed, including rejected (aborted) and continued takeoffs after a simulated failure of the critical engine. In plain words, the pilots evaluated behavior of the aircraft in a number of situations that might be observed in everyday airline practice. “We have tried a number of probable scenarios, both normal operations and failures. The inspectors were able to make sure that the airplane’s behavior is fairly close to the predicted one as foretold with help of some calculations done before the flights,” Ostrovsky said.
The data gathered during the test campaign provided sufficient grounds to assert that the actual field performance of the An-148/158 family aircraft comes fairly close to the figures given in the airplane’s flight manual. The data collected is also applicable to the An-148-100, the baseline model in the family of aircraft. Degradation of An-158 payload-range performance to higher runway elevation corresponds to rates observed on Boeing and Airbus jetliners, said Antonov.