High-Density-Altitude Departure from a Confined Ridge Site
You are tasked with a day VFR passenger transfer from a ridge-top helipad at 6,200 ft elevation. The surface is a small prepared pad with a downslope on the departure side and rising terrain beyond it. The outside air temperature is 28 °C, and the pressure altitude equals the elevation. The helicopter's flight manual gives a maximum weight for out-of-ground-effect hover at these conditions of 1,180 kg. Basic empty weight is 1,010 kg, pilot 85 kg, three passengers totalling 240 kg, baggage 30 kg, and fuel 150 kg. The pad is too small for a running take-off, and the only clear departure path requires an out-of-ground-effect hover to clear a 12 ft obstacle before accelerating. Wind is calm. The passengers are tourists with no aviation knowledge, and one asks whether the aircraft is 'full'.
1. Calculate the take-off weight and determine whether the departure is legal and safe as loaded.
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Sum the masses: 1,010 + 85 + 240 + 30 + 150 = 1,515 kg. That is 335 kg above the 1,180 kg out-of-ground-effect hover limit for these conditions. Even ignoring the hover limit, the aircraft is far outside the performance envelope for a confined pad with no running take-off and an obstacle. The departure as planned is not legal and not safe. The remedy is not a small adjustment; you need to remove roughly 335 kg, which means either reducing fuel substantially (and accepting a shorter range or a refuelling stop), offloading passengers or baggage, or waiting for cooler conditions. Because the pad has no running take-off option and the departure requires an out-of-ground-effect hover, the hover ceiling figure is the controlling limit, not the maximum certificated weight. The correct answer is to refuse the departure as loaded and re-plan.
2. Explain the physical reasons why the hover limit, rather than maximum weight, governs here, and what performance factors you would quote to the operator.
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In an out-of-ground-effect hover the rotor must produce thrust equal to weight using only the air it accelerates downward; there is no ground cushion to reduce induced velocity and therefore induced power. As density altitude rises, air density falls, so for a given thrust the rotor must accelerate a smaller mass of air to a higher velocity, and induced power rises. Temperature at 28 °C at 6,200 ft gives a density altitude well above the elevation, worsening the effect. Add the need to hover with no translational lift, then climb 12 ft over an obstacle before accelerating, and the power required approaches or exceeds available power. The margin you must preserve is the difference between power required and power available, plus the ability to arrest a sink if the engine or rotor performance is less than expected. Quote to the operator the density altitude, the out-of-ground-effect hover limit, the actual weight, and the resulting excess of 335 kg. The judgement point is that the aircraft can be below maximum certificated weight and still be unable to fly the departure.
3. Give the load-plan options you would present, ranked, and the passenger briefing you would give.
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Ranked options: first, split the transfer into two rotations, carrying two passengers and their baggage per trip with reduced fuel; this preserves the hover margin and is the safest. Second, reduce fuel to the minimum for the route plus reserve and offload baggage, checking the new weight against 1,180 kg. Third, delay to early morning when temperature is lower and the hover limit is higher. Fourth, use an alternative departure site with a running take-off capability. Never accept a 'just enough' margin at a confined site with rising terrain. Brief the passengers honestly but calmly: the aircraft cannot carry everyone and all the bags in one lift at this altitude and temperature, so the flight will be in two groups; explain the seat allocation for the first group, the baggage that will travel, and where the second group will wait in the shade. Confirm seat belts and doors, and make clear that no one boards until you say so.