PPRuNe Forums - View Single Post - AW139 G-LBAL helicopter crash in Gillingham, Norfolk
Old 22nd Mar 2017, 12:45
  #848 (permalink)  
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The SAR modes will use other sensors (GPS, accelerometers, inertial nav, even doppler) to give the speed which is why they are allowed to control TU/TD at low speed.

If the aircraft had a low speed display (LVI or groundspeed on the PFD/ND) then it could be used by the pilot for low speed IF but whether such 'extras' would be specified during the certification process I don't know.
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