In august 2016, after the G-LBAL accident I wrote this message to AAIB web-team.
I never got an answer.
"I disagree with:
1) “a slight tailwind may have affected the
helicopter during its departure; this would be one cause of a late registering of airspeed
in comparison with other, into-wind, departures”
In my experience, late registering of airspeed happens in all confined/vertical/short-field procedures, with front wind, and with a maximum 10° nose down pitch as indicated by the RFM.
Attitude recovering from -10° to 0° is commanded by time (2 seconds) and not by airspeed, ground speed or outside visual references.
The manual dictates then that the 0° pitch must be maintained till Vtoss is reached.
Several seconds with 0° pitch are necessary before suddenly airspeed gets “alive” and goes, in a very short time and sometimes instantly, from zero to 40/50Kts IAS.
During night VFR departures from coastal helipads, visual references are actually lost at TDP.
Take-off procedure is then performed from TDP with the sole reference to instruments till modes can be engaged (Phase 5 software) only at 60Kts IAS.
Experience in these procedures during day VFR operations integrates the type rating training, giving the pilot the absolute trust in the effectiveness of the sequences, even during the zero kts IAS phase.
Moreover, cues for pitch and power index are available (when set) in the PFD during all the sequence from hover to Vtoss, no matter if day or night operations.
Therefore, Cat A take-off procedures are actually performed with reference to instruments even during day VFR operations.
RFM and TRI should emphasize that
- Category A take-off procedures are actually performed with reference to instruments even during day VFR operations
- Delay in IAS is usual in these procedures and should be ignored till it gets “alive”
In my opinion, to be discussed:
“Safety Recommendation 2015-025
The European Aviation Safety Agency should amend its definition of Vmini, to
provide a clear definition that reflects the legitimacy of flight under instrument
flight rules by reference to external visual cues at speeds below Vmini.”
As per AW139 RFM, external cues are not utilized after TDP to perform a correct Cat A vertical/confined/short-field take-off."
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