turbulence

TURBULENCE IN FLIGHT

EASA at EPAS Volume III includes three safety issues concerning weather phenomena.

  1. Adverse convective weather (turbulence, hail, lightning, and ice) (SI-0003) (CC effect)

This safety issue addresses the ability and capability of the flight crew to manage the entire flight, including dispatch, and the possibility to detect, avoid and/or mitigate the effects of adverse convective weather on the flight.

If not managed well, a flight crew may experience aircraft upset after being forced out of its flight envelope by a severe atmospheric phenomenon, or a significant degradation in performance or the handling qualities of the aircraft, or injuries due to abrupt movements.

It also reviews the requirements for the aircraft to fly in certain atmospheric conditions.

The main threats of convective phenomena affecting the flight, such as convective turbulence, up/down-drafts, wind shear, hail precipitation, lightning, and icing are reviewed in this safety issue.

  1. Turbulence encounters (SI-0003B) (CC effect)

Clear air turbulence and orographically induced turbulence (i.e. turbulence generated by high mountains) and mountain waves are weather phenomena that may result in aircraft upset or injuries/damage.

The issue also covers the preparation of the flight and the availability of information to enable the flight crew to foresee a possible encounter with such phenomena during the flight.

  1. Windshear (SI-0024) (CC effect)

The encounter with windshear on final approach, landing, take-off, and initial climb may lead to aircraft upset or runway excursions. Effective SOPs and training for the flight crew should be implemented by airlines to ensure that the flight crew are well-equipped to avoid or deal with those conditions.

Such efforts should also be supplemented by the detection of potential windshear by third parties, such as ATC, and the effective relay of this information to the flight crew.

Effects of climate change under scrutiny

With climate change:

  1. Severe convective storms may become more frequent and/or intense, and the safety risks caused by the associated threats for CAT aeroplanes may increase.

For example, some research works suggest a significant increase of hail precipitation with hailstone size exceeding 5 cm over Europe, and an increase of the lightnings activity and

  1. Moderate-or-greater clear air turbulence associated with jet streams may become more frequent in the future.

For example, some research works suggest a significant increase in the probability of encountering moderate-or-greater clear air turbulence at cruise flight levels over the North Pacific, Southeast Asia and the North Atlantic.

The significance and the severity of the consequences of turbulence are highlighted in the 2024 Safety Report of the Flight Safety Foundation:

“Turbulence: For the third year in a row, turbulence encounters were the most frequent accident type in 2024. Of the 132 airliner accidents last year, 33, or 25 percent, were related to turbulence, including one fatal accident.

In that event, one passenger died, and 30 people were injured when a Singapore Airlines Boeing 777-300ER encountered severe turbulence while en route from London Heathrow to Singapore.

After the pilots were informed there were injured passengers in the cabin, the flight was diverted to Bangkok, where it landed safely.

The following diagram shows airliner turbulence-related accidents from 2019 through 2024.

The 33 turbulence accidents in 2024 represent the highest number in a single year since 1982.

All of the turbulence-related accidents last year occurred in jet airliner scheduled passenger operations and all but one of them happened in the en route phase of flight, according to ASN data.

Fifteen of the 33 accidents occurred in North America, the most for any region.

The following diagram shows the 10 most frequently cited airliner accident categories for the period 2019 through 2024. These accidents account for the majority of all airliner accidents during the period.

Following the previous accident reports, IFALPA, Flight Safety Foundation, and IATA highlighted the risk of injuries posed by turbulence and outlined practical steps to mitigate it.

The paper stresses three pillars of mitigation:

  • turbulence avoidance strategies at flight planning stage,
  • ensuring passengers keep seatbelts fastened at all times while seated, regardless of the illumination of the “fasten seatbelt sign” and
  • effective and timely communication from the flight crew to cabin crew and passengers.

In Skybrary, a description of turbulence is included, where the various types (mechanical, convective and clear air turbulence)of turbulence are presented.

For more information on turbulence and steps to avoid it or deal with it when you face it, please refer to:

 

Useful links:

Aviation Weather Centre: World Area Forecast System, SIGMET

Turbli: Europe turbulence map

ECNWF: Clear air turbulence (CAT), 0-6km wind shear and MUCAPE

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