From section 1.18.5.5 of the TSB report
TC produced a concern paper which stated that 5 seconds was insufficient for the pilot to engage the MGB oil bypass switch. Requiring the pilot to action a system of this type in such a short time was considered unusual, and TC stated its belief that this function should be automated. Sikorsky's response was to explain that 5 seconds represented the worst-case scenario. TC did not agree with Sikorsky's position. In an effort to mitigate risk, TC requested that Sikorsky provide additional guidance that would help the pilot determine whether the switch was selected quickly enough to trap sufficient oil, and to monitor the health of the transmission in bypass mode. In response, Sikorsky revised the Rotorcraft Flight Manual (RFM) to identify the range of MGB oil temperature and pressure indications pilots should expect to see after the bypass switch had been activated. Sikorsky also identified symptoms which would warrant a "land immediately" situation. TC accepted the RFM revision and on 07 February 2005, the S-92A helicopter was granted a TC type certificate based on a validation of the FAA approval.
So even though TC identified the issue IMO they accepted a rather poor solution. They should have insisted on an automatic cooler bypass and looked more at the temperature readings in the event of total MRGB loss as witnessed during the total oil loss test on 06 August 2002. Were the FAA in attendance at that test? What exactly did TC witness in the level 2, nothing, just a paper review at SAC? Why did TC not review the concerns that the JAA had raised?
The JAA are stated in the report to have referred to the Blackhawk's track record but just how similar are the S92 and Blackhawk MRGBs to draw conclusions from this comparison? Did the Blackhawk MRGB have steel or titanium oil filter housing studs and/or the high filter changeout issues? How does the Blackhawk MRGB achieve 30-minute run-dry capability?
IMO each aircraft type should be reviewed and approved on its own merits with no "follow-through" credit assumed from previous/similar designs. This for me was a fundamental error by the FAA and TC.
History has shown how this type of design approval can have serious consequences e.g. Bristow 56C G-TIGK lightening strike back in Jan '95 when flying out to Brae "A" highlighting issue via change of tail rotor to composite carbon fibre and aluminium reinforcement edging. I worked with one of the PAX after that successful A/R and he told me first-hand how lucky they were and the skill the pilots showed to save their lives.
Looks like 15+ years later we're still making the same mistakes in this industry. This needs to change.
Safe flying
Max