With legal and grassroots challenges still nagging, Boeing has revived marketing efforts eight months after officially winning the $11 billion programme to supply 141 combat search-and-rescue helicopters to the US Air Force.
Boeing is to build 141 search and rescue helicopters for the USAF
The selection of Boeing's HH-47 Chinook for the CSAR-X award faces a rare second round of protests from losing bidders Lockheed Martin and Sikorsky, with a decision by the US Government Accountability Office expected in September.
Meanwhile, a growing chorus of commentators and lawmakers have joined the debate about the air force's choice of a heavylift, tandem-rotor aircraft for the search-and-rescue mission.
In response, Boeing went on the offensive on 10 July, rebutting widely reported claims by critics on two key points: rotor downwash speeds and brownout vulnerability.
The HH-47 will produce a maximum 59kt (109km/h) rotor downwash at mid-mission aircraft weight, beating the USAF's requirement by 6kt, says Boeing programme manager Rick LeMaster.
The maximum velocity occurs only in the zone below where the counter-rotating blades overlap, he adds, with downwash winds measuring 30-40kt elsewhere.
Moreover, Boeing claims that the HH-47 at the midpoint of a rescue mission creates a downwash velocity that is less than half that of the AgustaWestland EH101 and H-92 offered by Lockheed and Sikorsky, respectively.
This is because the Chinook's tandem-rotor spreads the thrust generated by the blades over a greater area.
The HH-47's "disc-loading is considerably less because it has a greater rotor disc area," LeMaster says. "This additional disc area means the weight of the vehicle is supported by more lifting surface, resulting in a lower downwash velocity under the aircraft where rescue operations take place."
Boeing also claims that widely reported concerns about the HH-47's brownout vulnerability are inaccurate. By incorporating the Rockwell Collins Common Avionics Architecture System cockpit and the Digital Automatic Flight Control System, the HH-47 will "be equal to or better than any rotorcraft flying today", Boeing says.
In January, US government auditors upheld protests filed by Lockheed and Sikorsky, reasoning that the Boeing bid was unfairly advantaged by a perceived flaw in the air force's evaluation criteria.
The USAF used a different aircraft - the smaller HH-60G - as a baseline to estimate future manpower costs to maintain the CSAR-X fleet.
Lockheed and Sikorsky both argued this gave Boeing's larger aircraft the upper hand, but the auditors faulted the USAF only for not giving the bidders advanced warning.
Despite finding no other flaws in the USAF's selection process, the auditors recommended that the losing bidders be given a second chance.
The air force complied with that request in the narrowest possible way, setting the stage for this next round of protests.
Rather than invite all-new bids, the USAF will only allow the competitors to suggest tweaks to manpower-cost estimates, which constitute only a fraction of the overall costs of the programme.