Unfortunately, the history of aviation is full of fatal accidents. Let’s examine together one of these accidents, which resulted in the most deaths. As a result of this accident, a total of 349 people died in 1996 in over Charkhi Dadri, India.
On the evening of November 12, 1996, one of the deadliest mid-air collisions in aviation history occurred near Charkhi Dadri, approximately 100 kilometers west of New Delhi, India. Saudi Arabian Airlines Flight 763, a Boeing 747-168B, had departed Indira Gandhi International Airport on a scheduled passenger flight to Dhahran, Saudi Arabia, with Jeddah as its final destination. At the same time, Kazakhstan Airlines Flight 1907, an Ilyushin Il-76TD carrying passengers from Shymkent, Kazakhstan, was descending toward New Delhi. At approximately 6:40 p.m. local time, the two aircraft collided in mid-air, killing all 349 people on board. The disaster became the deadliest mid-air collision in aviation history and exposed critical weaknesses in altitude monitoring, cockpit coordination, and aviation safety systems.
At approximately 6:40 p.m. local time, the two aircraft collided in mid-air near Charkhi Dadri, Haryana. The impact caused both aircraft to break apart and crash to the ground. All 312 people aboard Saudi Arabian Airlines Flight 763, including 289 passengers and 23 crew members, lost their lives. The 37 occupants of Kazakhstan Airlines Flight 1907 also perished, bringing the total death toll to 349. Air traffic controllers lost contact with both aircraft following the collision. The disaster remains the deadliest mid-air collision in aviation history and one of the most significant accidents involving failures in altitude separation and aviation safety defenses.
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How They Collided
Following the collision, an official investigation was launched to determine the causes of the accident. Investigators examined the aircraft’s flight recorders, air traffic control communications, and the instructions issued to both flight crews. At the time of the accident, Saudi Arabian Airlines Flight 763 had been instructed to maintain 14,000 feet (FL140), while Kazakhstan Airlines Flight 1907 was cleared to descend to 15,000 feet (FL150), providing the required 1,000 feet of vertical separation. However, Delhi air traffic control relied on primary surveillance radar, which did not provide controllers with aircraft altitude information. Consequently, controllers depended on altitude reports transmitted by the pilots rather than independently verified radar altitude data. The investigation found that the controller had issued appropriate altitude instructions and did not identify an air traffic control error as the primary cause of the collision.
Investigation and Sequence of Events
Following the accident, the Government of India established a Court of Inquiry headed by Justice Ramesh Chandra Lahoti of the Delhi High Court. The investigation examined flight recorder data, air traffic control communications, crew actions, and the operational circumstances surrounding the collision. Particular attention was given to the altitude instructions issued by Delhi ATC and whether both aircraft had maintained their assigned flight levels.
On November 12, 1996, Kazakhstan Airlines Flight 1907, an Ilyushin Il-76TD, was operating a passenger flight from Shymkent, Kazakhstan, to New Delhi. While descending along ATS Route G452, the crew contacted Delhi ATC and reported passing FL230 for FL180, approximately 74 nautical miles from the Delhi navigation beacon (DPN). The controller subsequently cleared the aircraft to descend to FL150 (15,000 feet) and instructed the crew to report reaching that level.
Meanwhile, Saudi Arabian Airlines Flight 763, a Boeing 747-168B, departed Indira Gandhi International Airport at approximately 18:33 local time, bound for Dhahran, Saudi Arabia. The aircraft followed the PARVI Standard Instrument Departure (SID) and was cleared to climb to FL140 (14,000 feet). When the Saudi crew requested a higher altitude, the controller instructed them to maintain FL140 and stand by for further clearance.
Both aircraft were operating along the same air corridor, G452, in opposite directions. By assigning FL150 to the inbound Kazakhstan aircraft and FL140 to the outbound Saudi aircraft, Delhi ATC established the required 1,000-foot vertical separation between the two flights.
As Flight 1907 approached Delhi, its crew reported reaching FL150 at approximately 46 nautical miles from DPN. The controller instructed the crew to maintain that altitude and advised them of the approaching Saudi Boeing 747 at their 12 o’clock position, flying in the opposite direction at FL140. The traffic was initially reported approximately 14 miles away.
The Kazakhstan crew requested clarification of the distance, and the controller repeated the information. As the aircraft continued approaching each other, another traffic advisory was issued, indicating that the Saudi aircraft was approximately 13 miles away at FL140. The Kazakhstan crew acknowledged the transmissions.
However, the investigation established that Flight 1907 did not maintain its assigned altitude. Flight recorder evidence showed that the Ilyushin descended below FL150 without authorization, progressively reducing the vertical separation from the Saudi Boeing 747. The aircraft descended through approximately 14,500 feet and continued toward FL140, where the Saudi aircraft was operating.
At approximately 18:40 local time, the two aircraft collided near Charkhi Dadri, Haryana, approximately 40 nautical miles west of Delhi Airport. Both aircraft sustained catastrophic damage and crashed to the ground, killing all 349 people on board.
The Lahoti inquiry concluded that the Kazakhstan Airlines crew’s failure to maintain its assigned altitude was the primary cause of the collision. The investigation also highlighted shortcomings in cockpit coordination and communication, while the absence of independent radar-based altitude monitoring reduced the opportunities for air traffic controllers to detect the developing conflict.
1996 Charkhi Dadri – Causes of the Collision
The root and approximate cause of the collision was the unauthorised descending by the Kazakh aircraft to FL-140 and failure to maintain the assigned FL-150.
At the end of the accident, the reasons that caused the accident are as follows:
- Insufficient English knowledge of Kazakhstan airlines team. That’s why he doesn’t understand the ATC instructions correctly.
- Inadequate management skills of Pilot in Command. Lack of CRM – crew resource management.
- Lack of situational awareness of Kazakhstan Airlines flight crew. They do not fully understand the seriousness of my condition.
- Shortcomings of Kazakhstan airlines team in ATC – Pilot communication techniques.
Lessons Learned from the Charkhi Dadri Mid-Air Collision
The Charkhi Dadri disaster demonstrated the importance of effective communication, altitude compliance, crew coordination, and modern safety technology. The accident highlighted several lessons that remain relevant to aviation safety today.
Aviation English and Communication
Clear communication between pilots and air traffic controllers is essential in international aviation. ICAO language proficiency standards, standardized phraseology, and proper readback and hearback procedures help prevent misunderstandings and ensure that ATC instructions are correctly understood and followed.
Altitude Compliance and Crew Resource Management
The investigation identified the Kazakhstan Airlines crew’s failure to maintain its assigned altitude as the primary cause of the collision. This emphasizes the importance of continuous altitude monitoring, effective cockpit coordination, and Crew Resource Management (CRM).
Radar Surveillance and Collision Avoidance
At the time of the accident, Delhi ATC relied on primary radar and pilot-reported altitude information. Secondary surveillance radar could have helped controllers identify the altitude deviation earlier. Additionally, neither aircraft was equipped with TCAS, which could have provided another layer of protection against a mid-air collision.
A Multi-Layered Approach to Aviation Safety
The most important lesson from Charkhi Dadri is that aviation safety must never depend on a single individual or system. Effective communication, disciplined flight operations, reliable surveillance, and collision avoidance technology must work together to prevent accidents.
The disaster remains a powerful reminder that even a single operational deviation can have catastrophic consequences when additional safety barriers are insufficient. Finally, even in the superficial evaluation we made above, we saw that there are more than one variable affecting the occurrence of the accident. Most incidents in aviation do not have just one cause. And when examining accidents, one should not look at them from a single perspective. In this regard, The “Swiss Cheese Model” developed by Prof. James Reason is an effective method for examining such events.
References:
- https://aviation-safety.net/database/record.php?id=19961112-0&lang=fr
- https://en.wikipedia.org/wiki/1996_Charkhi_Dadri_mid-air_collision
- https://indianexpress.com/article/long-reads/charkhi-dadri-worst-mid-air-collisions-9825707/
- https://migflug.com/afterburner/the-deadliest-midair-collision-in-history/