12 Nov, 2018
Aviators and their flying machines have had to cope with adverse weather since the dawn of aviation. Today, weather continues to be one of the most important factors affecting aviation, safety and efficiency. The skill and experience of pilots vary widely as do the capabilities of their aircrafts. High winds and turbulence tend to be manageable when a helicopter is in level flight, in which the helicopter maintains a constant heading and altitude, but have a stronger impact during take-off, landing and hovering.
In 2002, pop singer Shakira was riding in a helicopter that had to make an emergency landing onto a baseball diamond in the Dominican Republic. It was not adoring fans that forced her down, but strong winds and heavy rains. Any weather phenomena can have an impact on helicopters and it does not discriminate against future vice presidents or celebrities. A properly trained helicopter pilot should look at any weather condition (including sunny skies) with caution. Bad weather conditions are unpredictable and special precautions must be taken in order to ensure passenger safety and correct rotorcraft operation.
Winds and turbulence make for an uncomfortable flight. Extreme turbulence can exceed the aircraft’s structural design load and performance envelope, causing damage to airframe, power plant, and even rotorcraft loss. Helicopters are especially vulnerable at low altitudes in mountainous terrain because downdrafts can easily exceed a helicopter’s capabilities, potentially pushing it into the terrain. High gusting winds can cause rotor blades to flex enough during start-up to cause a helicopter to have a mid-air collision with itself, usually the tail boom, Turbulence can easily toss a light helicopter (and they are all relatively light) hundreds of feet up or down in seconds. Clear Air Turbulence (CAT) is the turbulent movement of air masses. CAT usually takes place in cloudless skies and at higher altitudes when a sudden disturbance in the air is caused by smallscale wind velocity gradients around the high-speed air of the helicopter’s fan. The high-velocity air comes in contact with much slower air, resulting in sudden air currents and turbulence around the helicopter. Turbulence is more of an impediment to the overall comfort of the crew and passengers than a specific safety concern.
Behind hills, high winds can create turbulence during hovering phase. In this situation, pilots have a key role to play as they will take the decision to fly out of the area if it becomes too risky.
Clouds and Fog
Clouds and fog can have a negative impact on helicopter flight. When the lack of visibility obscures towers, mountains or other vertical obstacles and the pilot is not using instruments to maintain situational awareness, then issues bound.
Flight into clouds or fog can cause the pilot to become disoriented and lose control of the aircraft. The majority of helicopters are VFR-only and operate at the very altitudes where fog develops.Weather minimums for helicopters allow pilots to operate in very low-visibility situations and unfortunately pilots can quickly get into situations that overwhelm the capabilities of the helicopter. ‘Scud running’ is a common occurrence in the helicopter community and has lead to many situations that usually have catastrophic results. The majority of helicopter operations require visual meteorological conditions (VMC), yet with the combination of the lower minimums, it can force pilots to push their luck.
Violent conditions in and around thunderstorms can exceed rotorcraft structural limits and bring a helicopter down in seconds. Extreme updrafts and downdrafts from thunderstorm turbulence can toss rotorcraft hundreds, if not thousands of feet up or down very rapidly. Hail also can damage or destroy the aircraft through engine flame out and foreign object damage (FOD) damage or structural failure, lightning can cause damage to aircraft components or avionics and, if encountered at night, can cause flash blindness to the crew.
Flying near a thunderstorm does not necessarily represent a major safety issue as long as the aircraft remains in VMC operation well outside of Cumulonimbus clouds, which produce thunderstorms and associated serious turbulences or lightning. They should be avoided as much as possible to prevent damage.
Ice can adhere to flight surfaces and change their aerodynamic properties, making them much less efficient in creating lift.
Ice and Snow
Light dry snowfall usually doesn’t impact helicopter operation, but on landing the same snow can easily turn into a white-out situation and endanger a safe landing. Wet snow and icing are a big issue.
An extreme condition of “freezing rain” can give a very rapid buildup of hard ice on blades and airframes that can cause some vibration or performance loss. Avoid freezing rain or fly out of it as soon as possible. Again, mission preparation and meteorology are key safety elements for all weather rotorcraft flight.
The primary capability that GPS brings to bear is extremely accurate position awareness. This is extremely helpful in inclement weather or if the visibility is poor, a quick look at a GPS map display can orient the pilot to his position in relation to the terraAs a complement to other navigation systems (DMap, radar and obstacle avoidance systems), GPS technology can help ensure the aircraft is navigated clear of obstacles.
Despite the popularity and success of instrumentation to assist pilots, there is no substitute for pilot intuition and the human element. Hardware, no matter how state-of-the-art, is a waste of capital without properly training the pilot in its proper use. Pilots must be aware of the dangers of each weather condition and have the training to avoid the weather if it is dangerous enough or recognize what is happening if they get into bad weather.
Launching into VFR flight in marginal conditions without a full ‘tool kit’ and a solid Plan B is inviting disaster.”
As human factors remains the major element to ensure safety, pilots have to first learn the basis of high-quality mission preparation. Which kind of weather is expected during the mission? What are the effects of such conditions in the handling of the aircraft? What is the procedure to apply? In this context, pilots must have very human decision-making training to make sure that the crew will not lose precious seconds in case of a critical situation. Flight simulator training are a must. Simulation reproducing bad weather conditions can contribute to placing the crew in real conditions. In particular, full motion simulators equipped with visualization can train the crew in inclement weather situations with no risk. Mission training, such as mountain flying training is equally beneficial.
Mark Rose, 35-year pilot and manager of Alpine Lift Helicopters in Albany, has advice regarding mountain flying training given to him as a young mechanic and pilot working in Alaska. “Always be in control of the flight, don’t let the mountain, the weather or the temptation to compromise do the flying for you,” he says. “Mentally commit to a safe plan and stick to it. In a pass situation, determine your out, fly one side of the pass to make a safe 180 turn as plan ‘A’, then focus on a clean safe turn at two or three times of translation speed with good visibility and side space at a flat altitude. When you are half way through your turn, take a look out your window and check to see if the pass is clear; if so great, you can make a simple 90-degree turn and go for it, but if the pass is full of crud, a simple 90-degree turn is your safe ticket out.”
While not entirely possible, simply not flying in bad weather may be the only way to truly avoid weather-related helicopter flight problems. Until then, treat every flight as an educational experience when you strap in, listen to your conscience, say to yourself ‘I am planning on a safe flight right now,’ before pitch pull.Clearly, a safe helicopter flight in any kind of weather begins and ends with sound aeronautical decision making.
