EC135
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Troubleshooting; Human-Machine Interface
Aircraft Equipment Problem Critical
General None Reported / Taken
Aircraft; Equipment / Tooling
HSI precessed 101 degrees in 34 minutes while static on roof top helipad. Unable to manually slew HSI; manual compass heading card slew panel NOT INSTALLED. Night flight conditions; [I was] unable to conduct IFR flight; IMC procedures or accept another flight request due to precession of HSI. [I was] unable to navigate with HSI. Dead reckon navigated from hospital to base. HSI began to correct 5 minutes into the return leg to base at a rate of 4 degrees per minute. I would like to point out that while the problem at this specific Medical Center is significant; it merely is the environmental precondition to a forthcoming unsafe act. This Medical Center is one of at least eight hospitals with known magnetic anomaly interference in our area of responsibility. This has historically never been a significant safety factor because the legacy Bell 222B/U model aircraft were all equipped with a slewable HSI. The introduction of new aircraft has created a supervisory precondition for unsafe acts by not properly equipping the aircraft with this function. The aircraft are a newer variant of the EC 135P2+; the advanced avionics and in particular the AHRS are of a different generation than those installed in the older aircraft. I have seen the HSI take as long as 20-25 minutes to fully recover. Pilots have had to reposition to another nearby landing site to wait out the correction to the HSI; before being able to return to their base in IFR conditions. By conducting a risk/benefit analysis; one could clearly see that the risk is the aircraft and the insufficient capability to correct induced anomalies. Inadequate supervision has failed to correct a known problem that has created a precondition for unsafe acts. In order to mitigate the risk; an aircraft modification should be performed to install the necessary HSI control panel. The expense is irrelevant when compared to the cost of preventing a mishap. While it is true that magnetic interference at some landing sites do create an environmental hazard to the aircraft navigation equipment; the latent factors are insignificant when compared to the known active equipment precondition. It would be unreasonable to think that the environmental impact created by at least eight hospitals in the area could be reduced or mitigated to no longer being a risk. It is reasonable to mitigate the risk and control the aircraft anomalies through an improvement to the IFR aircraft.
An EC-135 helicopter pilot reported an HSI precess while parked on a hospital's rooftop helipad which he was unable to correct because the aircraft lacked a compass slew function.