PPL Video Lectures (10 Jul 2020)

PPL Video Lectures covering Aerodynamics, General Knowledge, Performance, Meteorology And Navigation are now available through our website see front page for details.

× Welcome to the CPL Meteorology question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

Headwind and IAS

  • Posts: 63
  • Thank you received: 0

MissSoph created the topic: Headwind and IAS

I’m prob going to go dahhh when it’s explianed..
a decrease in IAS and increase in rate of decent.. why would this indicate a sudden decrease in headwind component during an approach to land ?

Please Log in or Create an account to join the conversation.

  • Posts: 474
  • Thank you received: 65

Stuart Tait replied the topic: Headwind and IAS

Wind shears which cause a drop in IAS on descent are sometimes called undershoot wind shears since their effect
on a landing approach is to cause the aircraft to lose lift and descend below the intended approach path.


Please Log in or Create an account to join the conversation.

  • Posts: 19
  • Thank you received: 0

abargri replied the topic: Headwind and IAS

I always get confused with this question too Stuart. I sort of understand the graphic, but would appreciate any advice on how I can understand this better.

Please Log in or Create an account to join the conversation.

  • Posts: 2125
  • Thank you received: 158

bobtait replied the topic: Headwind and IAS

One of the most important factors that contribute to the generation of lift is IAS. That is the combined effect of both the true airspeed and the ambient air density as it encounters the wing from the direction of flight. If you are parked stationary on the ground in a headwind, the IAS would be due only to the headwind and nothing else. If you are flying into a headwind the IAS is due to your forward motion PLUS the headwind which would have been present even if you were not moving.

If you were riding a push-bike into a strong headwind and the headwind SUDDENLY stopped, you would feel less wind in your face. A SUDDEN decrease in headwind causes a temporary drop in IAS because the inertia of the aircraft prevents it from suddenly increasing it's speed to compensate for the reduced headwind. Because IAS is an important contributor to the production of lift, a SUDDEN reduction in headwind will be accompanied by a sudden reduction in lift even though you have made no change in power or nose attitude.

This effect is called wind shear and it results in a loss of lift and an increased rate of descent. As the aircraft's inertia is slowly overcome, the IAS will gradually increase to it's original value even if the pilot makes no changes to power or nose attitude.
The following user(s) said Thank You: abargri

Please Log in or Create an account to join the conversation.

Time to create page: 0.319 seconds