Many aircraft accidents each year are caused by encounters with unseen airflow hazards near the ground such as vortices, downdrafts, low level wind shear, or turbulence from surrounding vegetation or structures near the landing site. While such hazards frequently pose problems to fixed-wing airplanes, they are especially dangerous to helicopters, which often have to operate in confined spaces and under operationally stressful conditions (emergency search and rescue, military operations, shipboard operations).
The difficulty with airflow hazards is they are invisible, and thus the pilot may not be aware of being about to fly into "bad air." Pilots learn to rely on performance charts, operational envelopes, and their intuition, but nevertheless, lives are lost and millions of dollars in aircraft damage sustained each year due to vortex and downdraft encounters.
In the accident video above, unfortunately the crew of the helicopter did not survive. When this accident was analyzed, it was determined that aerodynamic effects over that section of the deck may have been a contributing factor to the accident. If the pilot had had some warning that there was a hazard in that location, he might have been able to take appropriate action in time.
Technological advances in sensor technology, especially Doppler lidar and PIV (Particle Image Velocimetry), offer the potential for helicopter-based sensors which can gather such airflow data in real-time. Within a few years, it may be possible to gather and display real-time airflow hazard data to pilots in the form of visual cues presented on a head-up display.
The volume of potentially useful data is vast and yet the pilot has only seconds or even fractions of seconds in which to consider and learn from it. Our challenge lies in developing a visualization that presents the critical information to the pilot in real-time and that enhances rather than degrades pilot performance.
By means of a series of usability studies, we developed an airflow hazard visualization system that, when presented to pilots in a high-fidelity rotorcraft flight simulator, significantly improved their ability to land safely under turbulent conditions.
Although operating a helicopter into or out of a confined area is always challenging, landing a helicopter on shipboard is probably one of the most hazardous of all aircraft operations .
|The Navy helicopter-ship so-called "dynamic interface" is also an ideal environment in which to study and attempt to ameliorate the risks caused by invisible airflow hazards. Because the ship is moving, its superstructure will always generate an air wake consisting of vortices and other unseen hazards. Due to the dangerous nature of the situation, the Navy has conducted significant numbers of ship-helicopter compatibility trials and therefore very large amounts of data from wind tunnel model-scale testing, full-scale flight testing, and computational fluid dynamics are available.||
Currently the main airflow-hazard information provided to
Navy helicopter pilots operating off of aircraft carriers is a flight
||which provides a "go/no go" decision based on wind velocities derived from shipboard anemometers (which often have significant errors) and the results of the above-mentioned flight testing, wind tunnel testing, and CFD. The Navy dynamic interface flight test program is a major effort that produces a great deal of information on shipboard conditions, helicopter limitations, and potential airflow hazards. However, communicating this information to pilots in the most useful way in the constantly changing shipboard environment is an ongoing challenge.|
Unfortunately, helicopter accidents and incidents occur each year, such as the accident described above, or other incidents such as "tunnel strikes" (when a rotor blade strikes the fuselage of the helicopter). There have been about 120 tunnel strikes since 1960, causing damage ranging from $50-$75K to over $1M; about ¾ have been shown to have been due to airflow hazards . When analysis of these accidents and incidents is performed, the conclusion is frequently that they were due to unseen airflow hazards such as vortices, downdrafts, hot exhaust plumes, or wind shear, where the pilot and ground crew were initially unaware of the danger and the pilot was unable to react in time. Presenting the appropriate information to the pilot or flight-deck air boss in advance of the hazard encounter could reduce or prevent these types of accidents in the future.
Most related research falls into one of the following categories:
It has long been recognized that applying developing technology to improve aviation displays might enhance aviation safety. Significant work in this area includes synthetic vision and augmented-reality displays (terrain in low-visibility environments, navigation aids) [6, 7, 8, 9], weather visualization including NASA's AWIN, TPAWS and AWE [10, 11, 12, 13], and turbulence detection/prediction . Holforty's research on wake vortex visualization  is one of the first to provide three-dimensional hazard cues with the intent of eventually layering the cues on an augmented-reality display. There is also a large body of relevant work concerning human factors in the cockpit, including the study of attention and cockpit visual displays [16, 17, 18, 19].
Also, it has been known since the eighties that weather-related airflow phenomena such as microbursts and wind shear have been responsible for the loss of hundreds of lives in airliner accidents . As a result, a great deal of work has been done to detect, predict, and display this type of information to the pilot . There are commercially available aircraft-based, forward-looking microwave radar and lidar systems that can detect microbursts and windshear. However, the emphasis was placed on integrating the information into existing cockpit displays, in order to reduce time to commercial deployment.
Providing helicopter pilots with flight-deck visualization that a hazard exists may be of significant benefit. However, the form such a visualization might take, and whether it does indeed provide a benefit, had not yet been studied before our work.
We developed an airflow hazard visualization system in accordance with user-centered design principles, and performed a series of usability studies, including a flight simulation study with experienced military and civilian helicopter pilots. To present the visualizations to the pilots, we modified the source code of a state of the art commercial rotorcraft flight simulator built by Advanced Rotorcraft Technology, Inc.  that has the capability of modeling both the helicopter flight characteristics as well as the ship air wake data. For our current study, we utilized archived data gathered from flight tests, wind tunnel tests, and computational fluid dynamics (CFD) provided by NAVAIR Advanced Aerodynamics Branch Patuxent River, MD [22, 23, 24].
Data was gathered both subjectively from the pilots' evaluations of the visualizations (including pilot ratings of landing difficulty, etc.), and objectively from the pilots' performance during the landing simulations. Dependent variables recorded by the flight simulator included velocity and position of aircraft in x, y, z, control stick position both lateral and longitudinal, collective and pedal positions, and landing gear forces.
Sixteen military and civilian helicopter pilots with a wide range of experience participated in our flight simulation usability study. Results showed a significant increase in the pilots' ability to land safely during simulated hazardous conditions. For hazardous landing approaches in highly turbulent conditions, the presence of a visual hazard indicator reduced the crash rate from 19 percent to 6.3 percent. (A "crash" was defined as an impact with the ship deck of greater than 12 feet per second as measured by the simulator.)
We developed an airflow hazard visualization system for helicopter pilots by following user-centered design principles. In a flight simulation usability study, our system significantly reduced the crash rate among experienced helicopter pilots flying a high fidelity, aerodynamically realistic fixed-base rotorcraft flight simulator into hazardous conditions.
We focused on one particular aviation application, but the results may be relevant to user interfaces in other operationally stressful environments.