When encountering a windshear, which instrument will change indication first?

2 Answers

1. 
   

   
   

   Skyfox on Jan 25, 2016

   It’s hard to give an exact answer because it depends on the direction of the wind change as you cross the shear boundary. A tailwind that shears to a headwind will cause the airspeed indicator to go up, as well as cause a sudden climb that affects the VSI and attitude indicator. A headwind that shears to a tailwind will do just the opposite. A sideways wind shear may not affect the airspeed indicator at all and may not change the amount of lift enough to affect the VSI, but will cause a big change to the attitude indicator as it catches the wings and tail and tosses the airplane around. A vertical shear like an updraft (ie. from wind blowing up the slope of a mountain ride you’re crossing) or a downdraft (ie. getting caught in a microburst at cruise altitude) will drastically affect the VSI and attitude indicator, and again may not do much to the airspeed indicator.

   Is the question you present from an exam or something? If so, I’d be curious to know what the source is.

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2. 
   

   
   

   Skyfox on Jan 25, 2016

   My apologies for answering twice but I have an addendum to include with my first answer. According to the Gleim instrument written test prep:

   “When climbing or descending through an inversion or wind shear zone, you should be alert for any sudden change in airspeed.”

   And from the Jeppesen Instrument/Commercial Manual:

   “It [wind shear] can subject your aircraft to sudden updrafts, downdrafts, or extreme horizontal wind components, causing loss of lift or violent changes in vertical speeds or altitude.” and “A horizontal wind shear can result in a sudden change in indicated airspeed.”

   From the King instrument instructor course book:

   “When a headwind shears to a constant tailwind, the characteristics observed will be: pitch attitude decreases, required thrust increases then decreases, vertical speed increases, indicated airspeed decreases then increases to approach [or cruise] speed.”

   From the ASA Private & Commercial Pilot’s Manual (Trevor Thom):

   “When climbing or descending through a windshear zone, you should be alert for sudden airspeed changes. Flying into a suddenly decreasing headwind on approach, for instance, would cause a sudden loss of airspeed.” [There’s no mention of the effect on instruments by changes to crosswind.]

   The Pilot’s Handbook of Aeronautical Knowledge and the Instrument Flying Handbook (FAA-H-8083-15) say pretty much the same thing as these sources and don’t list specific instrument effects like what you’re looking for. I hope this all helps!

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