Wednesday, October 1, 2008
Training: Safety Up High: An Alternative Look at Power Management
The school that teaches U.S. Army aviators to operate safely on high-altitude missions, like those on the battlefields of Afghanistan, shares key principals of that training.
Mid-October in the Rocky Mountains is no place for an outing by yourself, especially if you are unprepared. Typically during this time, pilots at the High-Altitude Army National Guard Aviation Training Site (HAATS) would spend their search-and-rescue time looking for lost hunters.
Not so in 2007. Two out-of-state hikers decided to climb the Mount of the Holy Cross near Leadville, Colo. They were armed with only tennis shoes and a pack of cigarettes on this particular day for what should have been a day hike to the summit and back. One of the hikers picked up the pace back to camp on the way down only to stop at a second trail head to wait for his friend, who never arrived. Ground teams began searching the following day as 18 in of snow fell in the first snow of the year in the high country. The next day a Bell Helicopter OH-58A was dispatched from HAATS to aid in the search.
The first mission of the aircraft was to insert a total of six individuals and one search dog to a location that searchers believed the day before contained a fire from the lost individual. The landing zone would be at about 12,500 ft msl in fresh powder and swirling winds. With the lost individual expected to be bewildered by hypothermia at this point, there isn’t a lot of time to debate if the aircraft can make it or not. There is no room for guessing.
Two passengers and a medium-sized search dog were loaded onto the aircraft and, without incident, were inserted into the LZ, followed by a second and third lift of two passengers each. Shortly after their arrival, the lost soul was found close to another ground crew and was taken to safety. Frostbitten on his ankles and suffering from hypothermia, this man lived to tell his tale. Others are not so lucky.
How is it that the pilots were able to land a fully loaded OH-58A at more than 12,500 ft in swirling winds and white-out conditions? The answer is that they didn’t think they could make it, they knew it! They were able to place ground teams in a position to affect a rescue and save this individual’s life instead of becoming victims themselves.
This was not magic and they weren’t reckless in their actions. It was a result of understanding three principal points as part of power management not often discussed: the environment, the aircraft, and themselves.
First, they understood the environment. Not simply because the Holy Cross is in their backyard, but they understood its winds and the density altitude. Winds move over and around obstacles in a consistent, and therefore, predictable manner. Understanding the mechanical turbulence created by these winds allows a pilot to avoid "bad air" or downdraft/turbulent areas that require extra power to overcome and could result in loss of aircraft control. It also helps the pilot to stay in "good air" or the updraft sides of canyons and valleys and provides him with a safety margin by reducing induced drag on the rotor system. This can provide usable power that would not normally be present on a day without wind, given the same density altitude. Winds also played a part mitigating whiteout on short final to the LZ by keeping the snow cloud generated by the rotor wash behind the pilot’s field of view. This allowed the pilots to attempt the landing with less than out-of-ground- effect (OGE) power available because they could use the ground effect safely.
Density altitude is another factor of the environment that is critical to understand. The aircraft is only going to provide a finite amount of power. An increase in pressure altitude and an increase in temperature reduce the amount of power available for the pilot to use. Though in this case, there was increase in the pressure altitude by being at 12,500 ft MSL, the temperatures in October, especially after a cooling snow storm, did not increase the density altitude to the point where a safe landing could be accomplished with the given loads. Aviators correct for density altitude in their performance planning, whether they realize it or not, any time they use temperature and pressure altitude to determine a power number. This was also true in the tabular data used to determine the power numbers for this mission.
They also understood the aircraft. A single-engine OH-58A is capable of some amazing feats if you understand what it takes to fly it. The pilots understood that there would be no OGE power available to get into the LZ, which may have been a factor if the winds were lighter (due to whiteout) or the LZ was a small confined area (possibly requiring OGE power to depart). Neither was the case such that the pilots were able to make a controlled approach and use in-ground-effect (IGE) power to gently set the aircraft down. The OH-58 also has a "caution" located in the performance-planning section of the operator’s manual that is often seen, but seldom remembered. It states, "Low-altitude maneuvering flights at airspeeds below 35 kt are not recommended under conditions where power required to hover OGE exceeds maximum continuous power [available]." It is a flight condition that is not often encountered, so it typically is not remembered. But it applied in this condition, as it often does during search and rescue operations in the high country.
This caution, coupled with the knowledge of how to avoid loss of tail-rotor effectiveness (LTE), was in the back of the pilot’s minds as they maneuvered in the search area with two searchers and a search dog on board. They mitigated this problem by avoiding downdraft and tailwind conditions and maintaining airspeed, especially while turning in the canyons and valleys.
Third, they understood themselves. While most aviators don’t like to admit it, we all have personal limits. It’s a matter of understanding where your personal envelope of abilities exists. Knowing where these personal limitations are will help you make smarter and safer decisions. This is extremely important with single-pilot aircraft. There is nothing wrong with admitting that you have never done this kind of mission or task before or that this is outside your comfort level. To expand your envelope of abilities, you train with a seasoned professional on the tasks you have never done before. Someone wanting to learn how to fly in mountainous terrain or overwater operations would not go out with a flight instructor who had never done these tasks. With a flight crew of more than one person, knowing your personal limitations will allow you to draw upon the experience level of the whole crew. The goal of the "understanding themselves" point is to not be the limiting factor in success or failure. If your performance planning says the aircraft can do the task required, the pilot — as a professional aviator — should not be the limiting factor.
Power management and the tactics techniques and procedures to accomplish it can’t really be summed up in one article. Each aircraft and each condition provides its own challenges. The three points that are fundamental to the understanding of power management apply to all aircraft and pilots. Understanding and applying knowledge of the environment, the aircraft and yourself may mean the difference between making a successful rescue or becoming a victim.