Delta

Man Made Turbulence

In this scenario a major company built an Industrial Facility adjacent to a non-towered municipal airport. The new facility had smoke stacks and large cooling towers. The stacks and the cooling towers created plumes of updrafts that drove complaints from pilots about significant turbulence experienced on final approach to the airport.

Weather

Instrument Meteorological Conditions (IMC) or Visual Meteorological Conditions (VMC)

NAVAIDs

Instrument approach procedures to the runway in line with the hazard

Airspace:

Class G

Findings

  • The source of the turbulence was located in line with the final approach corridor for the main runway.
  • The hazards were located at a distance that would cause an aircraft on final approach to experience turbulence at an altitude of approximately 350 ft. AGL based on 3-3.5 degree glide slope.
  • Company representatives and a consultant evaluated the turbulence by flying through the plumes to quantify the phenomena.
  • Aerodynamic forces experienced while flying through the turbulence was greater than 2G lasting more than a few seconds.

Analysis

  • Company representatives and a consultant evaluated the turbulence by flying through the plumes to quantify the phenomena.
  • Aerodynamic forces measured while flying through the turbulence were greater than 2G lasting more than a few seconds.
  • The analysis completed on the facilities behalf concluded that the hazard was no different than typical turbulence experienced by aviators on a summer day.
  • Even the smallest aircraft would not encounter forces exceeding aircraft design criteria.
  • The Facility weighed the risk of an accident occurring compared to the cost of paying for construction of a new runway and moving instrument approach equipment to it. They decided to accept the risk

Comments

The Facility contacted the local airport and requested that the presence of the hazard be broadcasted on the airport's Airport Surface Observation Station (ASOS).

Although experienced pilots complained about significant turbulence caused by the plume, one would expect that those pilots could respond safely to an aerodynamic upset associated with it; even a pilot with minimal experience should be able to cope with the hazard if it were known. However, this particular airport serves all facets of general aviation including student pilots.

A review of the case discovered that the Facility was unaware of the many official government methods for publicizing the hazard, which includes NOTAMS, sectional chart depiction, and airport information publications. Also, the Facility, having good intentions, was not aware that broadcasting the hazard on the ASOS would not reach all airport users since the airport was uncontrolled and aircraft radios are not mandated. While a reasonable person would find it obvious that failing to publish hazards is unsafe to air navigation, unknown hazards can be perilous to inexperienced pilots.

A “text book” scenario of fatal accidents involving inexperienced-pilots are stall-spin crashes on short final approach. It is unfortunate that the location of this hazard is exactly in the area where this type of accident occurs. Is it feasible to consider that an inexperienced pilot could lose control while encountering turbulence (up to two Gs) in a low, slow approach, near stall condition while over-shooting the runway centerline? Since management of the facility was fully aware of the hazards associated with the plumes, should a crash occur, would the company be culpable of contributing to it?