Safe Flying in Unsafe Weather  

By By Mark Robins | July 1, 2011
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High winds and turbulence tend to be manageable when a helicopter is in level flight, but have a stronger impact during take-off, landing and hovering.  Russian Helicopters

In February 2008, Senators Joe Biden, Chuck Hagel and John Kerry, along with a three-star general, were riding in a helicopter that was forced to make an emergency landing at 10,500 feet in the middle of the Afghanistan mountains. No one was injured and the Associated Press reported at the time that, “the senators and their delegation returned to Bagram Air Base in a motor convoy, and left for Turkey.”

It was not the Taliban that forced them down, but a snowstorm. “The weather closed in on us,” Kerry told The Associated Press at the time in a phone interview from Turkey. “It went pretty fast and we were around some pretty dangerous ridges. So the pilot exercised his judgment that we were better off putting down there, and we all agreed.” 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 trepidation and 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 component damage 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,” says Samuel Evans, research associate at Pennsylvania State University’s Aerospace Engineering department and retired U.S. Army Colonel/Aviator. “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. It can’t be detected on conventional radar, however it can be remotely detected with instruments that can measure turbulence with optical techniques, such as scintillometers or Doppler LIDARs.

CAT usually takes place in cloudless skies and at higher altitudes when a sudden disturbance in the air is caused by small-scale 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,” says Mike McKinney, regional sales manager at Aspen Avionics in Albuquerque, N.M.

High winds and turbulence tend to be manageable when a helicopter is in level flight, but have a stronger impact during take-off, landing and hovering. “As soon as the helicopter weight or inertia allows maintaining a steady flight path, the bigger the helicopter, the steadier the flight,” says Gilles Bruniaux, vice president of operational fleet safety at Eurocopter. “In the same way, a pilot flying in turbulence will tend to reduce speed to give a greater power reserve to combat downdraughts.”

The natural stability of a helicopter itself is an essential element to ensure a good level of stability. Furthermore, some equipment, such as the autopilot, can assist pilots by significantly strengthening the stability of the aircraft.

“Behind hills, high winds can create turbulence during hovering phase,” Bruniaux adds. “In this situation, pilots have a key role to play as they will take the decision to fly out the area if it becomes too risky. They equally have to ensure a good preparation of the mission, as high winds by themselves are a planning issue but no problem.”

Flying through mountains poses unique challenges that inclement weather can worsen. Russian Helicopters

Clouds and Fog

Clouds and fog can have a negative impact on helicopter flight. “Flying through fog or heavy clouds (in nonicing conditions) is absolutely no issue; all helicopters can do that all day long,” says Evans. “However, 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,” says McKinney. “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.”

Instrument meteorological conditions (IMC) describes weather that requires pilots to fly primarily by reference to instruments, and therefore under IFR, instead of by outside visual references under VFR. IFR capability upgrades the cockpit with the instrumentation necessary for flying in clouds or bad weather. Pilots sometimes train to fly in these conditions with the aid of Foggles—specialized glasses that restrict outside vision, forcing the student to rely on IFR indications only.

“As soon as the minimum IFR conditions are met in terms of ceiling and visibility, the aircraft is equipped for IFR flight and the crew is IFR qualified, there is no problem flying in bad weather conditions by reducing speed and clearing of obstacles using navigation systems fully,” says Bruce Webb, chief pilot at American Eurocopter. “Otherwise the major risks experienced are controlled flight into terrain (CFIT).” This occurs when the helicopter is unintentionally flown into the ground or any obstacle like a mountain, as well as loss of visual references (LOVR) leading to a loss of control.

Violent conditions in and around thunderstorms can exceed rotorcraft structural limits and bring a helicopter down in seconds. Evans warns that 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,” cautions Jerry McCawley, pilot and flight safety engineer at Lockheed Martin. “Lightning can cause damage to aircraft components or avionics and, if encountered at night, can cause flash blindness to the crew.”

Lightning can have disastrous results on the electrical system and components of a helicopter should it strike. A lightning strike to the main rotor system can damage the structural integrity of a rotor blade, possibly the worst consequence. However, tests and experience have proven many helicopters can remain fully operational after lightning strikes. To prevent them, Eurocopter has implemented several design features into its helicopter mechanics and potentially sensitive items like rotor blades. “These components have undergone severe lightning tests to demonstrate their low vulnerability to lightning effects,” says Elio Zoppitelli, research programs manager at Eurocopter.

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. Additionally, emphasize the importance of helicopter mission preparation combined with meteorology forecasts. The installation of weather radar is very beneficial.   

Ice can adhere to flight surfaces and change their aerodynamic properties, making them much less efficient in creating lift.
Russian Helicopters

Ice and Snow

Light dry snowfall usually doesn’t impact helicopter operation. “In flight the flakes fly by without sticking to the aircraft and mimic the USS Enterprise doing warp speed through asteroids in space,” says Evans. “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. Ice can adhere to flight surfaces and change their aerodynamic properties, making them much less efficient in creating lift. Chunks of ice can shed from the rotor blade and get ingested in the engine, creating an engine stall situation or even hit the tail rotor.” Some helicopters, he adds, “have thermal device capability, but most systems are difficult to maintain and rarely work with enough consistency to create enough confidence in pilots to attempt to fly in icing conditions.” Penn State University is currently doing research on ultrasonic vibrations to de-ice rotor blades instead of the current thermal methods.

American Eurocopter’s Webb insists that even in icing conditions (air saturated with water, at a temperature between +5 and -10 degrees Celsius), a fully de-iced helicopter can fly. “Eurocopter’s de-iced helicopters offer de-icing on the air intakes, main rotor, tail rotor blades and rear stabilizer,” he says. “A difference has to be made between aircraft able to resist long enough to icing conditions to fly out the zone and those equipped to be able to operate within those hard conditions. For example, the EC225 has been specifically designed with the capability to maintain flight in known icing conditions and is perfectly adapted to missions occurring in such severe weather.”

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.

IFR arms pilots with the tools needed to fly safely in bad weather. All helicopters equipped for IFR flight generally have an automatic flight control system (AFCS—autopilot), which strengthens the helicopter’s stability capabilities and reduces pilot workload. If available, the upper modes of the AFCS (speed/altitude/direction control) boost helicopter performance. In combination with other radio-navigation systems such as VOR, distance measuring equipment (DME), automatic direction finder (ADF) and GPS, they decrease the pilot workload in inclement weather conditions.

In a more general approach, IFR assists in following routes with traffic control assistance as well as navigation systems. Also, transponders can transmit aircraft identification, and give its position to other aircraft and controllers. While IFR aids pilots flying by referring to instruments, it is not limited to flying in bad weather conditions. As an example, “de-icing capability is not required to be able to fly IFR missions,” says Eurocopter’s Bruniaux.

Garmin’s G1000H integrated avionics suite has a large moving map with 10-, 12-, or 15-inch displays that show weather conditions. Garmin

As a complement to other navigation systems (DMap, radar and obstacle avoidance systems), GPS technology can help ensure the aircraft is navigated clear of obstacles. GPS has to be linked to the flight management system and provides better precision than legacy radio-navigation systems.

The primary capability that GPS brings to bear is extremely accurate position awareness. “This is extremely helpful in inclement weather or at night in hazardous terrain,” says Aspen’s McKinney. “If the visibility is poor, a quick look at a GPS map display can orient the pilot to his position in relation to the terrain. Many current GPS units now have the capability to dynamically show terrain above the helicopter’s altitude with very good vertical altitude resolution, graphically showing the pilot what terrain around the helicopter is the most hazardous. This has both positive and negative consequences though because it can cause a pilot to once again push further into inclement weather than they previously would have.”

In October 2010, FAA proposed stricter rules for helicopter instrumentation including many to increase safety for medical helicopters after a recent spike in fatal accidents. One proposed regulation is a requirement that all air ambulance helicopters be equipped with an electronic system to warn of terrain or other obstacles. Another would establish stricter weather limitations for EMS helicopter pilots flying under VFR. Currently, those rules apply only when transporting a patient.

Additionally, there are numerous rules regarding weather in the FAA FAR/AIM manuals taught to every pilot and are considered required knowledge of any licensed pilot. “The FARs contain requirements for the aircraft, the pilot and the weather for the safe conduct of IFR operations,” says George Ferito, director-rotorcraft business development at FlightSafety Intl in Dallas. “The Airman’s information manual also contains a wealth of information concerning instrument flight.”

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,” Ferito says. 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.

“Abiding by well-thought out SOPs, along with pilot and weather minimums is mandatory,” Ferito adds. “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. “Briefings on the effects of lightning, rain ice and other extreme conditions have to be ensured,” says Patrick Le Barenchon, military operational marketing manager at Eurocopter. “IFR training and 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, Ore., 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 instrumentation, regulations and training can assist pilots to fly safer in bad weather, one company is urging pilots to not fly in bad weather at all. Three Robinsons (R22, R44 and R66) are not approved for IFR flight and are intended for VFR only. From 1979 to the mid 1990s, fatal accidents in the R22 and R44 due to weather hovered around 14 percent year after year. However, from 2007 to 2009, Robinson’s weather-related fatal accidents have more than doubled (29 percent).

“Many are instances of ‘get-home-itis,’ i.e., trying to get home, be it at the end of the flight, the end of the day or the end of the weekend,” says Tim Tucker, chief instructor at Robinson Helicopter. “This is a decision-making issue more than anything else. With GPS and altitude indicators in VFR ships, VFR pilots are comfortable with the ‘I’ll just give it a try’ or ‘I can always turn around’ kind of thinking and this is the first decision down the road to disaster.” VFR pilots “should determine, perhaps with the input of a flight instructor and based on their experience level, local weather patterns, terrain and the minimum weather they will fly in such as ceiling, visibility and winds for day and night flight. The idea being the decision has been made as to what weather you’ll fly in. Pilots just need the discipline to execute this decision. Without having determined a set of personal weather minimums, many pilots will find a way to convince themselves to ‘just give it a try.’”

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, Rose suggests that pilots “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, hang out with old conservative pilots and read up on this area.” Clearly, a safe helicopter flight in any kind of weather begins and ends with sound aeronautical decision making.

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