Charkhi Dadri, one of the worst mid-air collisions: What happened in the cockpit that day

The Indian Express’s sum of the November 12, 1996 disaster. Archive

“For immoderate aerial postulation controller, it’s the worst nightmare… a midair collision,” said aerial postulation controller V K Dutta successful the National Geographic series, Air Crash Investigation, talking astir the midair collision betwixt a Saudi Arabian Airlines Boeing 747 and a Kazakhstan Airlines Ilyushin IL-76 connected November 12, 1996, implicit Charkhi Dadri successful Haryana, astir 65 km westbound of Delhi.

Dutta should know. On the fateful day, helium was the attack controller connected work astatine the Indira Gandhi International Airport successful New Delhi and was successful interaction with the pilots of some the Boeing 747 and IL-76.

At 6.40 pm, the jets collided midair. The monolithic jets, covered successful flames, plunged into the mustard fields below, successful 2 wreckage fields 7 kilometres apart. All 349 radical connected committee some the craft were killed.

In 1996, I was a second-year undergraduate student. The twelvemonth before, I had logged implicit 150 sorties, strapped wrong a glider cockpit arsenic an NCC cadet astatine Bhubaneswar airport. Three IAF pilots were our instructors. The glider successful which we trained had 4 instruments: an aerial velocity indicator (ASI), a vertical velocity indicator (VSI), an altimeter and what was known arsenic a crook & gaffe indicator. I had not been adjacent a commercialized pitchy yet, permission unsocial measurement wrong one.

But the analog altimeter with 3 needles (shortest for thousands of feet, mediate for hundreds of feet, longest for tens of thousands of feet) successful our glider was the aforesaid 1 you would find successful immoderate cockpit with analog instruments, including large jets. So, I felt I had thing to accidental connected the Charkhi Dadri crash. I wrote a ‘letter to the editor’, The Telegraph, Kolkata, speculating not connected what could person caused the clang but each the ways successful which an altimeter tin amusement erroneous readings. After all, the 2 jets collided arsenic both, inadvertently, were astatine the aforesaid altitude. I would beryllium proven wrong, of course, my missive small much than a show of my youthful impetuousness.

I preserved the India Today contented connected the clang for respective years, flipping done it from clip to time. One of the photographs carried successful the contented was precise haunting: 3 rider seats from the Saudi jet, inactive joined together, recovered successful the fields upright, a lifeless rider occupying 1 seat.

The Indian Express devoted its full Page 1 to the tragedy. Among the stories was Ashwini Sarin’s poignant relationship of what helium saw astatine the tract wherever the wreckage of the Saudi airliner lay. “There are nary survivors here, cipher to archer maine what happened astatine that fateful moment, nary 1 to archer the story,” helium wrote.

The Indian Express’s sum of the November 12, 1996 disaster. Archive

November 12, 1996: The crash

Saudi Flight 763 was a scheduled rider work from Delhi to Dhahran successful Saudi Arabia, with 312 passengers and unit connected board. In the cockpit were 45-year-old Capt Khalid al-Shubaily, archetypal serviceman Nazir Khan and formation technologist Ahmed Edrees.

Kazakh Flight 1907 was a chartered formation from Chimkent successful Kazakhstan to Delhi. There were 37 tourists and unit connected board. In the cockpit were 44-year-old Capt Alexander Cherepanov, archetypal serviceman Ermek Dzhanbaev, formation technologist Alexander Chuprov, navigator Zhahanbek Aripbaev and vigor relation Egor Repp.

Dutta was the attack controller astatine Delhi airdrome astatine the time, guiding some aircraft.

An airspace is divided into segments, each handled by a antithetic controller. The operation controller handles craft successful the contiguous vicinity of an airport. The adjacent chunk of airspace is handled by attack controllers specified arsenic Dutta, guiding approaching oregon departing aircraft. Beyond the attack controller’s airspace, country controllers usher aircraft.

Kazakh Flight 1907 was flying astatine 23,000 ft, astir 74 nautical miles from Delhi airport, erstwhile its unit archetypal contacted Dutta. He cleared the formation to descend and support 15,000 ft.

According to each accounts – ATC transcripts and the Cockpit Voice Recorder (CVR) information from the 2 craft – aft takeoff, Saudi Flight 763 was archetypal cleared to alert astatine 10,000 ft and past astatine 14,000 ft. Dutta instructed the unit to support 14,000 ft and basal by for support to ascent higher.

In those days astatine Delhi airport, for some arriving and departing commercialized jets, determination was lone a azygous corridor. The different corridors were reserved for the military. Which means, the Kazakh and Saudi jets were flying towards each different successful the aforesaid aerial corridor from other directions. Which is why, Dutta instructed the Kazakh unit to support 15,000 ft and the Saudi unit to support 14,000 ft to guarantee the mandatory 1,000-ft separation betwixt the jets erstwhile they crossed paths.

Delhi airdrome past was equipped lone with a superior radar. It did not person a Secondary Surveillance Radar (SSR). With a superior radar, controllers tin lone spot connected their surface the assorted craft contiguous successful the airspace without immoderate different information.

An SSR works differently. It automatically engages with the transponder connected committee an craft and relays captious details similar the aircraft’s identity, position, altitude, velocity etc to the controller. With an SSR, a controller request not inquire a aviator astir the aircraft’s altitude, nonstop presumption etc.

Working with lone a superior radar, Dutta depended connected the pilots of the Kazakh 1907 and Saudi 763 to cognize their altitudes. Both unit acknowledged Dutta’s instructions to support 15,000 ft and 14,000 ft, respectively. “Saudi 7 six 3 (will) support 1 4 zero (14,000 ft),” the Saudi unit acknowledged. This was their past transmission to the ATC.

“Kazakh 1907, present reached 1 5 zero (15,000 ft)…,” acknowledged the unit of the IL-76, which was present 46 nautical miles from the Delhi airport.

Dutta had to instrumentality the pilots’ connection connected the aircraft’s altitudes. Without an SSR, helium had nary mode to independently verify if the altitudes helium had assigned were being complied with.

As some jets flew towards each other, Dutta warned the Kazakh pilots of the Saudi pitchy approaching them, “Roger. Maintain 150. Identified postulation astatine 12 o’clock, reciprocal Saudi Boeing 747, 14 miles. Report successful sight.”

Here’s what Dutta’s transmission meant:

Clock codification method is wide utilized successful aviation to place different postulation successful the vicinity visually. Imagine a timepiece face. Imagine your craft arsenic a dot astatine the centre of the timepiece face, its chemoreceptor pointing towards 12.

“Roger. Maintain 150.” (Kazakh pilots are told to support 15,000 ft.)

“Identified postulation astatine 12 o’clock.” (On a timepiece face, Saudi pitchy was astatine 12 o’clock presumption comparative to Kazakh jet.)

“Reciprocal Saudi Boeing 747, 14 miles.” (Saudi pitchy was flying towards Kazakh pitchy connected a reciprocal absorption — other of Kazakh jet’s absorption — and was 14 miles distant from Kazakh jet.)

The Kazakh unit responded, “Now looking 1907.” That was their past transmission to the ATC.

The ATC portion transcript shows that the formation unit of the Saudi Arabian formation had fto retired a supplication successful those last moments, seeking forgiveness from Allah: “Ashhadu an la ilaaha illallah.”

The aviator of an USAF cargo flight, which was descending into Delhi and was successful the vicinity of the Saudi and Kazakh jets, archetypal alerted Dutta astir the midair collision. “We saw thing to our right, looks similar a large fireball, looks similar a large explosion,” the aviator told Dutta.

In the aftermath, the Directorate General of Civil Aviation appointed Capt K P S Nair, lawman director, Flight Crew Standards, arsenic Inspector of Accident.

What the probe found

The authorities acceptable up a Court of Inquiry led by Delhi High Court’s Justice R C Lahoti, who was assisted by Capt A K Verma, Director (Air Safety), Air India, and Air Cmde (retd) T Pannu, erstwhile director, operations (ATC), IAF.

The probe did not find immoderate responsibility with Dutta and said helium had fixed close instructions to some formation crew. The enquiry did not find immoderate responsibility with the instrumentality oregon the altimeters either.

It held that the midair collision happened due to the fact that the Kazakh pilots did not support their assigned altitude of 15,000 ft and descended to 14,000 ft.

In the people of the inquiry, the investigators discovered thing unusual. The Kazakh jet, though assigned to alert astatine 15,000 ft, had sliced the Boeing 747, assigned to alert astatine 14,000 ft, not from supra but from below.

The enquiry recovered that astatine 1 constituent erstwhile the Kazakh unit acknowledged that it was astatine 15,000 ft, the aircraft’s existent altitude was 16,439 ft. Prior to impact, the Kazakh pitchy had descended to 14,000 ft.

As recorded successful the CVR, 4 seconds earlier the jets collided, Repp, the vigor relation connected the Kazakh aircraft, saw the Saudi pitchy coming and shouted, “Get to 150 (15,000 ft), due to the fact that connected the 140th, uh that 1 uh…!”

Why would specified an experienced unit perpetrate specified a fatal error?

There was nary mechanical nonaccomplishment oregon defect successful either of the aircraft. There was nary responsibility connected the portion of Delhi ATC. Investigators focused their attraction connected the Kazakh unit and what went connected successful the cockpit successful those last seconds.

It recovered that it was Repp, the vigor relation of the Kazakh flight, who was communicating with Dutta. Repp sat down the pilots, facing sideways. He did not person an altimeter successful beforehand of him to cheque the aircraft’s altitude. He needed to glimpse implicit the enarthrosis of the skipper oregon co-pilot to spot the readings connected their altimeters.

Inside the cockpit, determination was nary verbal acknowledgement from the pilots that they had heard Dutta’s connection with Repp and understood it. Investigators recovered shortcomings successful Capt Cherepanov’s leadership, and the connection and teamwork among the unit of the Kazakh aircraft.

Another imaginable crushed for the Kazakh pitchy deviating from its assigned altitude, investigators felt, could beryllium the pilot’s mediocre proficiency successful English, who whitethorn person misunderstood the altitude assigned to the Saudi pitchy arsenic his own.

Kazaki authorities, defending the pilots, argued that the pitchy was incapable to support 15,000 ft and mislaid tallness due to the fact that of turbulence. It was ruled retired by the inquiry.

Recommendations for the future

The enquiry made respective information recommendations to forestall specified an mishap successful future, among them, equipping large airports with SSRs and abstracted aerial corridors for arriving and departing aircraft.

Neither the Saudi pitchy nor the Kazakh pitchy were equipped with Traffic Alert and Collision Avoidance System (TCAS). The onboard instrumentality automatically monitors different craft successful the vicinity and resolves imaginable conflicts without waiting for ATC guidance. For example, if 2 planes are connected a clang course, TCAS connected 1 craft volition inquire the unit to climb, portion TCAS connected the different craft volition inquire the unit to descend. The enquiry recommended the mandatory fitting of TCAS connected aircraft.

The writer is Deputy Associate Editor, The Indian Express, and an aviation enthusiast