Category A Vertical Takeoffs and the H-V Curve
Geoffersincornwall and Shawn Coyle are right on target, citing “the dynamics of the situation” and that “the Category A profiles will have been flown and tested to be safe.” A helicopter climbing vertically through a 100 ft TDP is in a substantially different energy state than a helicopter hovering at 100 ft.
Subsequent to single engine failure during vertical climb through 100 ft the pilot can lower the collective stick to contain the rotor droop while the helicopter continues to ascend to its peak height. By the time the descent begins, the remaining engine will have spooled-up and the rotor speed set to just below the governed speed thereby providing that OEI maximum contingency power is available throughout the descent. That’s why helicopters like the EC155 with Certified Category A helipad procedures can climb vertically to a TDP on the order of 100 ft, and successfully land back. This will have been demonstrated at up to the maximum helipad takeoff weight for altitude and temperature by both the helicopter manufacturer and the certificating authority prior to achieving Category A certification approval.
I have not seen the EC155 Category A Helipad Flight Manual Supplement, but it’s hard to believe that it doesn’t address this issue. This is addressed for other helicopter models. For instance, in the Limitations section of the S-76C+ Category A Helipad Supplement it states that “using the procedures and gross weights described in this supplement, it has been demonstrated that safe operation within the avoid area of the height-velocity diagram can be maintained if a single engine failure occurs at any point along the takeoff and landing flight paths.”