Saturday, October 1, 2005
Helping Aircrews Survive Brownouts
The U.S. Army is assessing a new system designed to enhance situational awareness for CH-47D and UH-60A/L crews during brownout and other degraded visual conditions.
Several articles and letters have been written over the past months describing brownout and discussing methods to overcome this significant threat to helicopters.
For instance, U.S. Air Force Lt. Col. Steve Colby challenged industry "to develop technologies in affordable packages for aircraft without highly advanced navigation systems or databus architecture" ("Help With Brownouts," March 2005, page 42). One such technology has been integrated and flown in brownout conditions: the Brownout Situational Awareness Upgrade (BSAU). Designed for the Boeing CH-47D and Sikorsky UH-60A/L, this system is the result of a development effort initiated more than 18 months ago in response to input from the field and lessons learned from Afghanistan and Iraq. The goal, as defined by the U.S. Army's Cargo and Utility program management offices, was a system that enhanced crew situational awareness in a degraded visual environment. The Aviation Applied Technology Directorate was brought on board to develop, integrate, and test this system.
That directorate set forth attempting to maximize the use of qualified military hardware and applying the best attributes of proven commercial technologies. Block I of the program focused on providing flight symbology for the CH-47D and UH-60A/L. As symbology systems have long flown in the Boeing AH-64A/D and various special operations aircraft platforms, there was ample data on symbology layouts, sensors, and displays. Using this, team members focused on optimizing the symbology set for landings and takeoffs in a brownout. This is something quite different from the design philosophy of previous systems. While success hinged on creating a responsive, intuitive low-airspeed symbol set to combat brownout, the integration of sensors and components to drive the symbol set remained paramount.
An initial crew-station working group created a draft symbology layout. With this defined, each symbol was traced back to a sensor or input critical to drive the selected parameter with the required precision and accuracy. This linkage, from sensor to symbol to display, formed the basis of the initial system architecture. An iterative process of test, fix, and test was then used to drive the design to a workable symbol set and final system architecture. Keys to this were verifying the accuracy and precision of the input data, ensuring an intuitive display (and thus reducing the pilot's cognitive workload) and optimizing the input and symbol sensitivity to allow for smooth and precise control inputs.
In the end, the original symbol set, along with several sensor inputs, had been significantly modified. This again reinforced how complex and difficult the transition from paper to application can be. The team also assessed techniques, procedures, training requirements and sustainability and maintainability issues.
The final BSAU Block I system consisted of a blended inertial-GPS, low-speed symbology set driven by a Honeywell Embedded GPS/INS (EGI) standard navigator and displayed on a Rockwell Collins multi-functional display (MFD). This replaced the analog horizontal situation indicators (HSIs) in both pilot stations of the UH-60A/L and CH-47D. The symbology could also be displayed on an EFW flat day heads-up display (FDH) that connects to the standard NVG mount for the HGU-56P helmet or as a selectable page on the current AN/AVS-7 heads-up display.
The real test of the system's attributes came during actual brownout landings at Yuma (Ariz.) Proving Grounds' Kofa Dust Course, noted for having brownout conditions most similar to Iraq and Afghanistan. Day and NVG brownout approaches were flown. Test cameras captured views of each approach from outside the aircraft, from the pilot's canopy and from over the pilot's shoulder (to captures the MFD symbology). The views from outside the aircraft depict the magnitude of the brownout condition. Likewise, the view from the pilot's canopy was severely degraded in terms of visual cueing and a lack of outside visual references to assist with descent rate, lateral drift, and aircraft attitude. As the aircraft descended through 15 ft AGL and began to encounter the dust cloud, the symbology continued to provide those critical elements necessary to retain situational awareness. As the aircraft decelerated, the system automatically scaled in velocity, providing better resolution to the aircrew. Then, monitoring heading, velocity, lateral drift, and rate of descent, the pilot successfully continued the approach to the ground with minimum forward airspeed and lateral drift. While the system proved its value, good crew coordination, briefing of "go around" procedures, and power management still remained critical tasks.
No level of technology can be successful without proper aircrew training. Crews must not only understand how to manage the system, they must be confident in the accuracy of the information presented, their ability to intuitively and correctly assess the aircraft state, and then decisively apply the appropriate action. While the BSAU Block I system isn't a "silver bullet" guaranteed to eliminate brownout incidents, testing has shown it significantly increases aircrew situational awareness during degraded visual operations. Coupled with the right techniques, procedures, and training, it should prove a tremendous aid in attacking brownout.
Inception to execution of NVG brownout landings with the upgrade took only seven months. Even with the success of this rapid prototyping initiative, the Aviation Applied Technology Directorate continues to pursue other technologies to better enhance aircrew situational awareness. Current programs include integration of long-wave forward-looking infrared (flir) sensors and 94-GHz radar. During the previous brownout testing, two infrared cameras were installed on the UH-60A evaluation aircraft and included in the Yuma Proving Grounds evaluation. These results, along with the 94-GHz radar test results, will better assess the optimum mix of fused "see through" technologies and flight symbology.
Finally, flight control augmentation remains another viable avenue to combat brownout. Currently, a newly integrated digital automatic flight control system is being tested on the CH-47D. Additionally, the Aviation Applied Technology Directorate continues to investigate use of a hover-coupler system for the UH-60A/L. These systems could well prove to be other successful methods to attack brownout.
Lt. Col. Patrick H. Mason is the former chief of the Prototyping and Integration Section of the U.S. Army's Aviation Applied Technology Directorate at Fort Eustis, Va.