Graham Warwick/ATLANTA

SELECTION OF the Raytheon Aircraft Beech Pilatus PC-9 MkII for the US Joint Primary Aircraft Training System (JPATS) surprised almost everyone - except, that is, the company itself. Throughout the competition, and the protests which followed, Raytheon remained steadfastly confident in the strength of its proposal.

That confidence has been vindicated, with rejection of the final protest against its selection, and award of the hard-won $4 billion contract to produce 712 aircraft for the US Air Force and Navy.

Pundits argued that the USAF would not accept a turboprop trainer. Reports claimed that all four jet powered contenders, were rated ahead of the Beech MkII in flight evaluations, by USAF and USN pilots. Still Raytheon remained convinced that a turboprop's lower acquisition price and life cycle cost represented the best value. "We knew we had a great aircraft - the best aircraft," says Raytheon chief executive Art Wegner.

The Beech MkII was named as the JPATS winner in June 1995. Protests were expected, given the magnitude of the contract, and they came, first from Rockwell, then Cessna. Both had offered jet trainers and each argued that the choice of a turboprop signified that there had been an unannounced shift in the selection criteria, from "best value" to "lowest price".

Cessna claimed additionally that results from the flight evaluations had been manipulated unfairly and that the Beech MkII could not meet the requirement to accommodate a wide range of student-pilot sizes. When these claims became public, the normally stoical Raytheon was stung to respond that Cessna's allegations were "irresponsible and absolutely false".

The USAF says that the US General Accounting Office rejected both protests after "...validating both the [source-selection] process itself and the Government's decision to select the Beech MkII". According to the service, the aircraft meets or exceeds the JPATS specification, at low life-cycle cost, with "exceptional" handling characteristics, while exceeding requirements to accommodate small female students.

Explaining Raytheon's decision to base its bid on the Pilatus PC-9, vice-president, JPATS programme, David Reimer highlights "...the $500 million life-cycle-cost difference in fuel burn between a jet and a turboprop". He says that the PC-9 offered "excellent" spin characteristics, which were carefully maintained during Raytheon's "missionisation" of the aircraft to meet the JPATS specification.

The changes proved substantial. Handling characteristics were improved, pressurisation introduced, bird-strike protection increased, zero-zero ejection seats installed, and single-point pressure refueling added. A "glass" cockpit was developed, using commercial cathode-ray-tube and liquid-crystal displays. The engine was up-rated.

The Beech MkII is powered by a 1,270kW (1,700shp) Pratt & Whitney Canada PT6A-68, derated to 820kW, whereas the PC-9 has a 705kW PT6A-62. The larger engine increases sustained-manoeuvre performance, while derating reduces life-cycle cost, says Reimer.

Propeller torque-effects are an inherent disadvantage of turboprop trainers, which Raytheon has tackled using an engine power-management system. This provides a linear power response matching that of the P&WC JT15D turbofan (see diagram), and masks the slower engine spool-up and rapid "kick-in" of propeller pitch of a typical turboprop, Reimer says.

In addition, a trim-aid device balances rudder, aileron and elevator trim requirements to reduce pilot workload. This reduces propeller torque-effect, allowing the aircraft to be flown "feet on floor".

Meeting the legislative requirement that the cockpit be capable of accommodating students ranging from a 1.93m/115kg male to a 1.24m/50kg female, "...was the biggest design challenge", Reimer says. "As the seat rides higher it moves away from the controls, and as it moves lower it gets closer," he explains. The USAF says: "The Beech MkII exceeds the Congressional mandate of safely accommodating 80% of the eligible female population, and it also achieves 97% anthropometric accommodation."

During the JPATS competition, Raytheon modified one PC-9 to a Beech MkII engineering prototype and built two production prototypes. Now it has a contract for one manufacturing-development aircraft, plus options for the first 141 production aircraft. Deliveries are scheduled to begin in early 1999, to the USAF, with USN deliveries beginning early in 2002. The USAF will receive 372 aircraft to replace 40-year-old Cessna T-37s, while the USN will take delivery of 339 aircraft to replace 30-year-old Beech T-34s.

Production for the US services is set to continue to 2017. Raytheon is pursuing export orders, with several countries having indicated a preference to follow the US lead

Under its original 1990 agreement with Raytheon, Pilatus was to produce the Beech MkII wing. This was amended in 1993 to allow Raytheon to build the entire airframe, with the Swiss manufacturer receiving a royalty.

Source: Flight International