National 8 (Spotlight Weekly)

CFIT Again

Despite growing awareness of the risks, Controlled Flight Into Terrain remains the key cause of air disasters

By KESHAB POUDEL

In thick fog and rain, a Twin Otter aircraft of Skyline Airways crashed at Surkhet, 400 kilometers west of Kathmandu, killing all four people on board, including two crew members. According to preliminary reports, the ill-fated aircraft hit the 6,500-feet Rani Matta Gargar hill 10 kilometers from Surkhet airport.

Aeroplane journey : question of safety

Like almost all other Twin Otter crashes in the last 20 years, the Skyline aircraft hit the mountain before turning into pieces along the ridges of the mid-western region. This is the second accident of Skyline Airways caused by Controlled Flight Into Terrain (CFIT).

The main cause of air accidents in Nepal is reported to be CFIT, which means the pilot was in control when the aircraft hit the mountain in bad weather. Over 80 percent of the world's air crashes are caused by CFIT.

Eye-witnesses reported that there was a blanket of thick fog on the mountain at the time of the crash. Although the aircraft was equipped with Global Positioning System (GPS), which explains the distance and track of the aircraft, crew members monitored the height through the altimeter.

The causes of most accidents in Nepal follow a similar pattern. But nobody seems serious about averting recurrences. Two years ago, the Civil Aviation Authority announced a program to reduce air accidents, but it could not be properly implemented.

Experts argue that such accidents can be averted by strictly following flight rules and regulations. The aircraft that flies in Visual Flight Rule (VFR) must avoid fog and clouds, as it is based on "see-and-seen" basis. If the aircraft enters the fog and cloud, it has to maintain its height until it cross the condition. According to aviation experts, once the aircraft uses the GPS, it must fly completely under the VFR and Visual Meteorological Condition (VMC).

But many crew members are used to flying under the Instrument Meteorological Condition (IMC). The rule is that once the aircraft flying under the VFR rule enters clouds, it must use GPS and maintain a safe height. The GPS provides better navigational aid to the aircraft flying in VMC mode.

Aircraft that use Instrument Flight Rule (IFR) can fly on IMC, but most aircraft in Nepal which are supposed to fly in VFR does not use VMC. If a crew member reads the altimeter and uses the GPS and flies in VMC, CFIT accidents can be averted, as the pilot knows the track, distance and altitude.

Unfortunately, crew members calculate timing based on experience. "If the plane enter a thick fog, it must fly maintaining a safe height," said a civil aviation expert. The rule is that an aircraft flying in complete VFR using GPS must take safe altitude. Studies have shown that CFIT accidents were caused due to overconfidence of the crew members."

Although some experts argue the need to use Ground Proximity Warning System to avert crashes, it cannot be used in most of the non-pressurized aircraft like Y-12 and Twin Otter, which operate in the terrain. The optimum service ceiling of the Twin Otter is 11,600 feet. Due to the requirement of oxygen and the topography of the mountain, these aircraft have to limit their height to 10,000 feet. If GPWS is used in such aircraft, it will issue warning continuously and make flying impossible.

In most cases, crew members apply their experience in landing and maintaining height when the weather conditions are severe, instead of going to a safe height. It is said that accidents have been avoided by properly applying available navigational equipment. At airports in Surkhet, Jumla, Lukla, Bajura, Bajhang, Jomsom, accidents were caused by human error. If the crew wants to fly on their own experience, VMC is must.

On the way to Surkhet from Jumla, Skyline Airways' Twin Otter lost contact with Surkhet control tower just three minutes before landing. Tower officials at Surkhet Airport sent helicopters in search operation.

As long as human judgment is the basis for flying, instead of using the available safety navigational facilities to read altitude, distance and track, one cannot avert CFIT accidents. This requires a massive awareness campaign.

In 1999 alone, the crashes of Necon Air's Avro in Ramkot, Lufthansa B727 in Bashmasur Danda, RNAC's Twin Otter in Dadeldhura and Skyline Airways' Twin Otter in Makwanpur were caused by CFIT. The time has come to devise ways of preventing such human error.