UPDATED: More Turbulence–Nine Passengers Injured on Cathay Pacific Flight from San Francisco to Hong Kong on 19 Feb.
This topic is among several key Cabin Safety Issues which will be addressed at the upcoming IATA Cabin Safety Conference in Madrid, this 20-22 May. Flight Chic will be there, and furnishing readers with live updates and detailed articles.
On February 18, Passengers on United Airlines Flight 1676, suffered a harrowing experience when their flight destined from Denver to Billings, Montana encountered turbulence. Several passengers and crew were seriously injured and had to be sent to hospital.
On February 19, the FAA issued an Advisory Circular 90-23G on Aircraft Wake Turbulence. As described by the FAA, the circular “presents basic information on wake vortex behaviour, alerts pilots to the hazards of aircraft wake turbulence, and recommends operational procedures to avoid wake turbulence encounters.”
Image: Illustration of the Wake RollUp process from FAA AC 90-23G.
The circular goes on to detail the dynamics of wake vortices in great detail, stating that “The worst case atmospheric conditions are light winds, low atmospheric turbulence and low stratification (stable atmosphere). In these atmospheric conditions, primarily in en route operations, vortices from Heavy and especially Super aircraft can descend more than 1,000 feet.”
The timing of the release of this AC is curious, in light of yesterday’s accident. While coverage is that United Airline’s safety team is still assessing the situation, clearly more is happening behind the scenes.
The circular opens up the possibility that present incidents of injuries through turbulence may be attributable as much to procedural deficiencies, when guiding the flight paths and overlaps of various sizes of aircraft sharing the airspace, as they are to atmospheric conditions. In layman’s terms, this is a problem which is not entirely arbitrary, and associated risks may be manageable with adequate procedures in place.
Leafing through the 18 pages of the AC, plus its accompanying appendices, is a bit daunting, but hidden among the technical language is a section which may reveal some of what happened yesterday; at the very least it is one procedural area which the FAA felt required sufficient clarification for them to issue a new regulatory document.
The FAA spells out shared responsibilities for ATC and pilots stating:
“Air traffic controllers apply procedures for separating instrument flight rules (IFR) aircraft that include required wake turbulence separations. However, if a pilot accepts a clearance to visually follow a preceding aircraft, the pilot accepts responsibility for both separation and wake turbulence avoidance. The controllers will also provide a Wake Turbulence Cautionary Advisory to pilots of visual flight rules (VFR) aircraft, with whom they are in communication and on whom, in the controller’s opinion, wake turbulence may have an adverse effect. This advisory includes the position, altitude and direction of flight of larger aircraft followed by the phrase “CAUTION-WAKE TURBULENCE.” After issuing the caution for wake turbulence, the air traffic controllers generally do not provide additional information to the following aircraft.”
They include two strong notes:
NOTE: Whether or not a warning or information has been given, the pilot is expected to adjust aircraft operations and flightpath as necessary to preclude wake encounters.
NOTE: When any doubt exists about maintaining safe separation distances between aircraft to avoid wake turbulence, pilots should ask ATC for updates on separation distance and groundspeed.
While various climate factors outside the control of airlines and regulators will continue to plague aviation, changes in procedures and awareness of the risks can avoid severe injuries and save lives.
The incident on United Airlines Flight 1676 should make passengers mindful of the importance of donning seat belts at all times. The risk of injury during turbulence for a passenger wearing a seatbelt is significantly reduced. Crew members, however, especially flight attendants who need to be about the cabin at all times, are not offered the same protection. If turbulence strikes suddenly, as it did for UA 1676, they have no time to respond.
Changes to procedures for plotting flight paths are clearly necessary to ensure the safety of vulnerable crew. This AC is a good step forward in the process.