Instantaneous Winds

Instantaneous Winds

  • June
  • 20
  • 2023
  • Advanced Aircrew Academy

The NTSB published its final report of a 2022 runway excursion of a Hawker 800XP in Aspen, CO. They determined the probable cause was "The flight crew's improper decision to take off in tailwind conditions that exceeded the airplane's performance capabilities, which resulted in a runway overrun following an aborted takeoff."

The captain reported the airplane and runway were clear of any contaminants and all pre-takeoff checks were normal. When the airplane was cleared to taxi, the reported wind was from 170° at 18 knots and gusting to 30 kts. During the takeoff clearance for runway 33, the air traffic control tower reported the wind was from 160° at 16 knots, gusting to 25 knots, and the instantaneous wind was from 180° at 10 knots.

The captain performed a static takeoff and, at rotation speed, applied back pressure on the yoke; however, the airplane would not become airborne. The captain reported, "the yoke did not have any air resistance or any pressure on it as we experience normally in Hawkers." After a few seconds and without any indication the airplane would take off, the captain aborted the takeoff and the airplane went off the end of the runway into the snow.

The NTSB noted in the final report that the "instantaneous wind" term is not defined in any FAA publication. "Because the ambiguous term is not defined in available resources, pilots that infrequently operate at that airport are likely not familiar with the definition and potential operational impact." The NTSB went on to comment the "flight crew failed to consider the constant wind conditions that were above the maximum tailwind limitation and decided to attempt the takeoff once they received an instantaneous wind report that did not exceed the tailwind limitation."

In Advanced Aircrew Academy's training modules, we review the various types of wind reports a flight crew can receive and how those wind reports are generated. When multiple reports are received with differing information, it is important to consider all sources along with visual indications (windsock) to base your decisions on.

  • METAR reports are a 10‑minute average wind.
  • ATIS or tower reports updating METAR information is a two‑minute average wind.
  • ATIS or tower reported gust is the wind peak value during the past 10‑minute period.
  • ATIS broadcast is updated when the wind direction changes by more than 30 degrees or if the wind velocity changes by more than five knots over a five‑minute time period.
  • If an instantaneous wind reading is desired and is requested from ATC, the phraseology "instant wind" should be used in the request. ATC may provide instant wind information without request under shifting/gusting wind conditions.
  • Instantaneous is measured in last three seconds.
  • Internal Reference System (IRS) in the cockpit is near‑real‑time wind.
  • Flight Management System (FMS) is a 30‑second‑average wind.