B737NG Vref Ice
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B737NG Vref Ice
Can anyone clarify whether Vref ice is applicable to a flap 15 landing in the following context:
The aircraft has initially taken off in icing conditions on the ground and, as per Vol 1 SP.16 used both wing and engine anti ice. The WAI valve naturally closes at T/O thrust application and WAI switch clicks off at rotation.
The flight progresses to destination in little or no icing conditions and does not use WAI inflight.
My question really focusses on whether taxying is considered part of the flight where the QRH in any flap 15 landing NNC says "If any of the following apply, set VREF ICE:............wing anti-ice has been used at any time during the flight"
The common sense (rare sense) approach would say the extra ten knots is only added to ensure stall margin in the case of additional weight and aerofoil/ empennage airflow disturbance due ice buildup. But what I dont know is: Does the ADIRU stall margin corrections added for the remainder of the flight after WAI use activate if the WAI switch is only on whilst the PSEU is in the ground mode? And either way, is this sufficient reason to add the 10kts if there is obviously no ice buildup on the wings (i.e. landing in 35 degrees centigrade)?
Thanks in anticipation,
Kind regards.
The aircraft has initially taken off in icing conditions on the ground and, as per Vol 1 SP.16 used both wing and engine anti ice. The WAI valve naturally closes at T/O thrust application and WAI switch clicks off at rotation.
The flight progresses to destination in little or no icing conditions and does not use WAI inflight.
My question really focusses on whether taxying is considered part of the flight where the QRH in any flap 15 landing NNC says "If any of the following apply, set VREF ICE:............wing anti-ice has been used at any time during the flight"
The common sense (rare sense) approach would say the extra ten knots is only added to ensure stall margin in the case of additional weight and aerofoil/ empennage airflow disturbance due ice buildup. But what I dont know is: Does the ADIRU stall margin corrections added for the remainder of the flight after WAI use activate if the WAI switch is only on whilst the PSEU is in the ground mode? And either way, is this sufficient reason to add the 10kts if there is obviously no ice buildup on the wings (i.e. landing in 35 degrees centigrade)?
Thanks in anticipation,
Kind regards.
Per Ardua ad Astraeus
Join Date: Mar 2000
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Good question! My (literal) reading of the manual is that this only occurs with the air/ground sensor in 'Flight', so the answer SHOULD be 'No', but as with all things, worth looking into!
WRT yr last paragraph, I understand that the 10 kts is to avoid the activation of the 'modified' stick shaker etc rather than because of aerodynamic disruption? I would hazard an answer that it is probably worth doing anyway AT ANY OAT/TAT for the trouble it will cause - that way all is covered?
NB The engine anti-ice will have the same effect if in use at the time.
Any Boeing experts here?
WRT yr last paragraph, I understand that the 10 kts is to avoid the activation of the 'modified' stick shaker etc rather than because of aerodynamic disruption? I would hazard an answer that it is probably worth doing anyway AT ANY OAT/TAT for the trouble it will cause - that way all is covered?
NB The engine anti-ice will have the same effect if in use at the time.
Any Boeing experts here?
Per Ardua ad Astraeus
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Whilst on this topic, would anyone else like to see the instructions on wing anti-ice re-written to say ' when WING icing conditions exist...' rather than '...when ICING conditions exist...' as I would rather it be left to the captain's discretion than to HAVE to put it on with an OAT of 9.9deg, in rain, and a wing temp of +5 deg?
At 'the end of the day' it matters not, but just seems unnecessary?
At 'the end of the day' it matters not, but just seems unnecessary?
