Business & GA, Commercial

Safety in Avionics: Let There Be Light

By David Evans | January 1, 2001

The fatal Oct. 31 crash of a Singapore Airlines jet while taking off at night in bad weather raises a basic issue of cockpit visibility, and whether it’s time to equip pilots with technology to give them a better view of the scene ahead.

It was the prototypical "dark and stormy night" when Capt. Foong Chee Kong advanced the throttles for the takeoff of Singapore Airlines flight SQ006. With typhoon Xangsane approaching, the windshield wipers beat out a rhythmic thwack-thwack as the B747-400, heavily laden with fuel for the long flight from Taipei to Los Angeles, began rolling down runway 05R at Chiang Kai Shek International Airport.

Visibility reportedly was about 1,600 feet (490 meters). Imagine Foong’s horror when a scoop loader parked on the runway loomed out of the darkness, right about the time when the accelerating jet was reaching takeoff speed. He instinctively reacted by rotating prematurely, hoping to clear the excavator, rather than aborting the takeoff and "soaking up the damage." Alas, the excavator’s cab tore into the jet’s underbelly, and its boom and bucket struck the left wing. The force of impact tore off the left engine, also amputating the bucket from the excavator’s boom. The airplane probably stalled, hitting the ground in a slewed attitude due to the asymmetric thrust, causing the fuselage to break into three pieces. Survivors reported great difficulty in opening exits–no doubt due to the twisting and distortion of a sideways "landing."

Thinking he was accelerating down the 12,000-foot Runway 05L, for which he had been cleared for takeoff, Foong had mistakenly turned too soon, onto the parallel 9,000-foot-long Runway 05R. Although closed for construction, the threshold markings remained in place, and the runway center line was illuminated.

At this point in the accident postmortem, it is too soon to assay whether Foong, his first officer, and the relief pilot in the cockpit were distracted by the driving rain and never noticed that they were turning onto Runway 05R instead of 05L. What they thought at the time will, in the fullness of the investigation, become known, as they lived through an accident that killed 81. It could have been far worse had the plane been carrying a full rather than a half-load of 159 passengers.

Maybe there is a way to enhance the pilot’s view in such circumstances. A technology has emerged that could help pilots see better outside the cockpit than with the unaided eye.

For years, the military has employed infrared search and track (IRST) gear to navigate safely during high-speed night attack runs at low level below the enemy’s radar and, in the target area, to designate targets for weapons delivery. The technology amplifies the heat signature of objects.

Indeed, this approach has found its way into the automobile industry, where Cadillac is now advertising an infrared view through the windshield for motorists travelling darkened nighttime roads. The advertisement shows otherwise invisible deer clearly visible on the road ahead.

The thermal signature, however, is severely degraded by moisture–a good reason the Cadillac advertisement extols the benefit of its infrared-vision option during dry driving conditions, sidestepping the diminished deer-spotting capability during a downpour.

Ah, but that Cadillac sensor and its more complex military cousins represent a so-called "passive" approach. The sensor looks ahead in the infrared wavelength. It does not light the way.

In this regard, an "active" sensor might go far to overcome the limitation of IR technology when buckets of rain are pouring or snow is falling with blinding intensity.

Jim O’Meara, president of Alaska-based Greatland Laser, a company developing the use of lasers to better mark runways, believes an airborne low-power laser scanning device, illuminating targets ahead, would be a valuable visual aid both on the ground and in the air.

His conceptual infrared laser scanner (patent pending, O’Meara notes) could be mounted on the chin of the aircraft under the radar, or in a small pod under the wing (see illustration). The pod would measure approximately 12 inches (30 cm) in length, 6 inches (15 cm) in width and some 4 inches (10 cm) high. Weighing about 2 pounds (0.9 kg), it would contain a low power (eye safe) laser. An oscillating mirror would cause the laser to scan out, covering the intended field of view. The laser would be aimed slightly down, below the horizon, continually scanning the area ahead, from a distance of just a few feet to a few thousand feet ahead of and to the sides of the aircraft.

O’Meara believes an active laser sensor, employed in concert with retro-reflective surfaces (such as the glass bead tapelines applied to highways), would provide a marked improvement to pilots’ situational awareness. Runway center lines, taxiway exits, other airplanes, ground equipment, and so forth could be outfitted with reflective tabs. "Painted" by the airplane’s scanning laser, they would show up brightly in a cockpit display. The laser-enhanced image could be incorporated into a head-up display (HUD) for ease of use during Category II and III approaches.

"The crew behind the lasers would be the only ones that see the retro-reflective return. It would be hardly noticeable to someone outside the cockpit and would never be seen by nor distract other aircraft crews or ground vehicle drivers," O’Meara asserted. "Prove this to yourself by taking a standard laser pointer out at night and shine it on a stop sign," he suggested. "It will appear brilliant to you, but a viewer several feet to the side of you would hardly notice it."

The oscillating mirror fulfills a specific purpose. "Aiming a laser and illuminating a target is difficult, but with the laser scanner, all retro-reflective targets in the scanning area are illuminated, regardless of their position," he explained. As an example of the system’s detection capability, O’Meara believes an IR laser could spot a target 5 miles (8 km) distant with visibility less than one-third of a mile (0.53 km).

While the system would not be impervious to inclement weather, O’Meara believes that a technique known as "range-gated imaging" would enhance the IR laser system’s ability to "see" through fog, rain and snow.

Now imagine if the runway centerline and edges at Taipei’s Chiang Kai Shek International Airport and the construction equipment parked in the gloom ahead had been marked with retroflective surfaces. As a first order, Foong might have noticed that the runway he was turning onto was narrow. The closed runway 05R was only 150 feet (48 meters) wide, whereas the open runway 05L was a good 50 feet (15 meters) wider. The temporary concrete barrier, the parked excavator and other construction equipment, stationed some 3,000 feet (915 meters) ahead, would have been visible, providing a second and more obvious cue that something was seriously amiss.

Foong reportedly uttered an expletive and declared "something there" too late in his takeoff run to avoid catastrophe. With an IR laser scanner, he might have realized his mistake and said the same thing as he lined up on the closed runway, but he would have cursed before acceleration, not after it was too late to stop. (For more on the concept, see www.greatlandlaser.com, or contact O’Meara by e-mail at laser@alaska.net .)

Aircraft Laser Scanner

How would a laser scanner on an aircraft work? Through a lens, the laser light is transformed into a horizontally expanding beam of radiation, which is reflected off a vertically oscillating mirror. The energy, then reflected off a fixed mirror, emerges as a vertically oscillating, horizontally expanding line beam of laser light through a heated glass window. The heated window is necessary to clear ice and frost.

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