Friday, October 20, 2017
Transport Canada - Aviation Safety Letter Jet Blast Hazard Issue 2/2010

Jet Blast Hazard Issue 2/2010

The following is published as a result of an Aviation Safety Information letter from the Transportation Safety Board of Canada (TSB).

On June 25, 2006, a Boeing B737-600 was cleared for takeoff from the threshold of Runway 26L at the Vancouver, B.C., international airport. At the same time, a Cessna 182 was stopped at Taxiway C; once the B737 began to roll, the tower controller cleared the Cessna 182 to taxi to position on Runway 26L and wait. The Cessna 182 taxied onto the runway immediately, and as it began to turn left to line up, the left wing lifted as a result of encountering the jet blast from the departing B737. The Cessna 182 sustained damage to its right wing tip and propeller.

Recorded radar data showed that the B737 was approximately 1 200 ft down the runway when the Cessna 182 encountered the jet blast. The Transport Canada Aeronautical Information Manual (TC AIM) (TP 14371E), section AIR 1.7 “Jet and Propeller Blast Danger” provides guidance to pilots to help them avoid jet and propeller blasts from other aircraft. A diagram in this section identifies the potential danger areas behind three representative types of turbo-jet aircraft, namely “executive”, “medium”, and “jumbo” jets, based on three engine-thrust rating levels: 10 000, 25 000, and 55 000 lbs, respectively. The depicted distances show the danger zones behind the three classes with their engines at both idle and take-off power settings. For example, behind a medium jet with an engine thrust rating up to 25 000 lbs, at take-off thrust, the danger area is 150 ft wide and extends 1 200 ft behind the departing aircraft. For a jumbo jet at takeoff, the danger area is shown as 275 ft by 1 600 ft.

The performance of medium jet aircraft allows them to also operate from smaller Canadian airports, where the greater population of light airplanes and helicopters operate, providing a varied mix of aircraft operations, in both size and performance. Many of these general aviation pilots have little experience operating behind these larger jet aircraft. The information provided in the TC AIM is therefore a vital aid for these pilots.

A review of engine thrust ratings for modern generation aircraft such as the Boeing B737-800, the B747-400, and the Airbus A320 shows that engine thrust has risen considerably over the years. As a result, it is not uncommon for a modern medium jet engine to produce considerably more thrust than the 25 000 lbs referenced in the TC AIM and for the heavy jumbo jet to produce thrust levels reaching 90 000 lbs. This significant increase in thrust ratings increases the danger area behind a departing modern jet. Accordingly, basing their decision on the data in TC AIM AIR 1.7, pilots entering a runway behind a medium jet, for instance, may encounter jet blast far stronger, for a longer time period, and at greater distances than depicted in the TC AIM. Therefore, there is an increased risk that a light aircraft could be damaged or upset by jet blast even though the current guidelines in the TC AIM were being followed.

Action taken by TC
As a result of this letter, the TC AIM section AIR 1.7 was updated and the following text was added:

As newer aircraft are designed to handle more weight, larger engines are being used. Executive jets may have thrusts of up to 15 000 lbs; medium jets may have thrusts of up to 35 000 lbs; and some jumbo jets now have thrusts in excess of 100 000 lbs. Therefore, caution should be used when interpreting the danger areas for ground idle and take-off thrust settings, as some of the distances shown may need to be increased significantly.

In addition, although the danger areas depicted in the diagram have not changed, the thrust figures have been updated to reflect the revised figures above.

Jet Blast Danger Areas (Not to scale)
Jet Blast Danger Areas (Not to scale)

Click on image to enlarge

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