An alternative take-off profile may be used when TODRH exceeds TODAH, such as in a helipad back-up manoeuvre.
The TODRH may exceed the TODAH, if the helicopter, with the critical engine failure recognised at TDP can, when continuing the take-off, clear all obstacles to the end of the TODRH by a vertical margin of not less than 10,7 m (35 ft). In addition the aircraft must be able to land back on the FATO in the event of an engine failure before TDP.
The aircraft must be able to fly the back-up manoeuvre with sufficient power margin and land back on the FATO in the event of an engine failure before TDP.
So, Hover Out-of-Ground Effect (HOGE) is required.
According to AMC1 CAT.POL.H.205 and CAT.POL.H.220 Take-off and landing - APPLICATION FOR ALTERNATIVE TAKE-OFF AND LANDING PROCEDURES:
(a) A reduction in the size of the take-off surface may be applied when the operator has demonstrated to the competent authority that compliance with the requirements of CAT.POL.H.205, 210 and 220 can be assured with:
(1) a procedure based upon an appropriate Category A take-off and landing profile scheduled in the AFM;
(2) a take-off or landing mass not exceeding the mass scheduled in the AFM for a hover-out-of-ground-effect one-engine- inoperative (HOGE OEI) ensuring that:
(i) following an engine failure at or before TDP, there are adequate external references to ensure that the helicopter can be landed in a controlled manner; and
(ii) following an engine failure at or after the landing decision point (LDP) there are adequate external references to ensure that the helicopter can be landed in a controlled manner.
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