Weather Hazard

          There are many different atmospheric elements that pilots and the aviation community will come into contact with when operating an aircraft. One of those elements are the unexpected weather conditions or conditional climate control that can affect the performances of an aircraft. In many cases, the severity of the different weather conditions can be scaled from either moderate to severe. In my opinion, thunderstorms are a weather hazard that poses the greatest risk to aviation operations. 

          All thunderstorms need the same ingredientsin order to form, which includes moisture, unstable air and lift. Moisture usually comes from oceans. Unstable air forms when warm, moist air is near the ground and cold, dry air is above. Lift comes from differences in air density. It pushes unstable air upward, creating a tall thunderstorm cloud. In most cases, thunderstorms are caused by cumulonimbus clouds. Like many clouds, the cumulonimbus develops when warm air rises from the surface of the earth. As the warm air rises, it cools, and water vapor condenses into minute cloud droplets. In a thunderstorm, the updraft of warm air is rapid, and the cloud builds up quickly.

         These type of clouds presents the most significant threats to aircrafts since it is known for producing thunderstorms, lighting,  hail, or tornadoes which can easily cause damage to an aircraft. They are also categorized as low-level clouds developing as low as 600m above the surface creating low visibility and turbulence; however, with its strong vertical updraft, they can extend well into the high bases and levels of clouds usually being smoothed or striated. 

Large hail stones found within large thunderstorms cells can cause structural damage to the aircraft and its engines. They have been known to cause damage to the leading edge of the wings and nose cone as well as crack the windshield and damage the engines.

         Severe icing is dangerous for commercial aircraft. Ice forming on the aircraft structure increase the weight of the aircraft, which in turn increases the stalling speed. It also disrupts the airflow over the wings, reducing the total lift produced by the wings. Lift created by the wings counteracts the weight of the aircraft which is what gets, and keeps the aircraft airborne. Most commercial aircraft are certified to fly through light to moderate icing but not severe icing. Pilots will therefore always look to avoid areas of severe icing. Thunderstorms can be particuarly dangerous as they may contain ‘Super Cooled Waterdroplets’. This is liquid which remains as a fluid despite it being below the freezing temperature. It freezes as soon as it comes into contact with a hard surface, like an aircraft, which can cause significant performance issues.

         In other cases, lighting from thunderstorms have struck commercial aircrafts while in the sky. The damage the aircraft receives from a lightning strike varies. The structure of the aircraft is designed to dissipate the electric charge overboard, but the entry and exit points can cause damage to the aircraft’s skin. It can also potentially interfere with the aircraft’s electrical systems but it rarely causes any significant problems.

Other threats or hazardous conditions that thunderstorms from cumulonimbus clouds poses includes:

• Precipitation like large raindrops, snow pellets and hailstorms

• High winds with speeds up to 150 knots that can damage the wings of an aircraft

• Updrafts or downdrafts (wind shear)

• Microbursts 

• Severe and extreme turbulence, and lastly

• Supercell thunderstorms that can form severe tornado's

All of which can be hazardous to commercial passenger jets. They have caused passenger jets to crash before, and could possibly be a contributory part in a crash in the future.

One way pilots avoid a thunderstorm when flying a plane is to fly on top of the thunderstorm. They also use air traffic control's help as well since they can see on the radar what a pilot cannot see out the window when flying through rain. Other ways for pilots to avoid cumulonimbus clouds or thunderstorms are:

• Preflight planning by checking the weather charts or websites

• In-flight weather services such as Hazardous Inflight Weather Advisory Service (HIWAS) and En Route Flight Advisory Services (EFAS)

• Weather Radar Technologies, and 

• Divert to an alternate airport if the storm systems are unpredictable or widespread.

If pilots cannot avoid the thunderstorm and have to fly through the embedded cell, the best way for them to safely endure and escape the hazard is to maintain a straight course through the thunderstorm rather than turning around. According to the FAA, A straight course minimizes the amount of time in the thunderstorms and turning only increases structural stress on the aircraft. This, however, is subjective and only for worst-case scenarios. Other approaches include:

• Disengaging altitude/speed hold on autopilot and focus on maintaining a level attitude

• Turn icing or anti-icing equipment

• Slowing airspeed to an appropriate turbulence penetration speed

• If There's Lightning, Don't Look Outside (it can blind you)

References:

Federal Aviation Administration. (2022). Pilot’s Handbook of Aeronautical Knowledge. FAA. https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/phak/media/14_phak_ch12.pdf

FlightDeckFriend.com. (2021, January 4). Are Thunderstorms Dangerous For Commercial Passenger Aircraft?FlightDeckFriend.Com | Pilot Jobs | Flight Training | Aspiring Pilots. https://www.flightdeckfriend.com/ask-a-pilot/are-thunderstroms-dangerous-to-aircraft/

What Causes a Thunderstorm? (n.d.). NOAA SciJinks – All About Weather. https://scijinks.gov/thunderstorms-video/