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Aviation Learning Center Document AC 61-134 - Controlled Flight into Terrain Awareness
Author: Federal Aviation Administration Date: April 1, 2003
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8. VFR-Only Pilots Operating in Marginal VFR/IMC Conditions.
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a. Operating in marginal VFR/IMC conditions is more commonly known as scud running. According to National Transportation Safety Board (NTSB) and FAA data, one of the leading causes of GA accidents is continued VFR flight into IMC. As defined in 14 CFR part 91, ceiling, cloud, or visibility conditions less than that specified for VFR or Special VFR is IMC and IFR applies. However, some pilots, including some with instrument ratings, continue to fly VFR in conditions less than that specified for VFR. The result is often a CFIT accident when the pilot tries to continue flying or maneuvering beneath a lowering ceiling and hits an obstacle or terrain or impacts water. The accident may or may not be a result of a loss of control before the aircraft impacts the obstacle or surface. The importance of complete weather information, understanding the significance of the weather information, and being able to correlate the pilot's skills and training, aircraft capabilities, and operating environment with an accurate forecast cannot be emphasized enough.

b. Continued flight in reduced visual conditions compounded by night operations and/or overwater flight poses some risks. VFR pilots in reduced visual conditions may develop spatial disorientation and lose control, possibly going into a graveyard spiral, or descend to an unsafe altitude while trying to maintain visual contact with the surface. The pilot then impacts terrain, the surface, or an obstacle while trying to maneuver. The following are some of the CFIT risks associated with such flight.

  • (1) Loss of aircraft control.
  • (2) Loss of situational awareness.
  • (3) Reduced reaction time to see and avoid rising terrain or obstacles.
  • (4) Inability of the pilot to operate the aircraft at its minimum controllable airspeed.
  • (5) Getting lost or being off the preplanned flightpath and impacting terrain or obstacle.
  • (6) Reduced pilot reaction time in the event of an aircraft maintenance problem because of a low or lowering altitude.
  • (7) Failure to adequately understand the weather conditions that resulted in the reduced conditions.
  • (8) Breakdown in good aeronautical decisionmaking.
  • (9) Failure to comply with appropriate regulations.
  • (10) Failure to comply with minimum safe altitudes.
  • (11) Increased risk of hitting one of many new low altitude towers installed for cellular telephones and other types of transmissions. This risk is especially great along major highways if VFR pilots try to follow a highway when lost or trying to stay under a lowering ceiling.
  • (12) Failure to turn around and avoid deteriorating conditions when first able.

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