Investigation Summary
Saudi Flight 763 had just departed Delhi and was climbing to FL140, while Kazakhstan Flight 1907 was descending to FL150. Due to a combination of poor English language proficiency among the Kazakh crew and a reliance on a single radio operator to relay instructions to the pilots, Flight 1907 failed to maintain its assigned altitude. Critically, the radio operator lacked his own flight instruments and had to look over the pilots' shoulders to read the altimeter, which significantly hindered his situational awareness and ability to verify the aircraft's actual level. The Ilyushin Il-76 descended into the path of the Boeing 747. The aircraft collided at an altitude of approximately 14,000 feet. The collision was exacerbated by the lack of secondary surveillance radar at Delhi, which would have provided controllers with precise altitude readouts for both aircraft.
Final Conclusions
The primary cause was the failure of the Kazakhstan Airlines pilot to follow ATC instructions, likely due to language barriers and inadequate CRM. Contributing factors included the absence of TCAS on both aircraft and the lack of secondary radar at Delhi Airport.
Video Analysis
The Worst Mid-Air Collision In The History Of Aviation | Mayday: Air Disaster — The Worst Mid-Air Collision In The History Of Aviation | Mayday: Air Disaster
If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
TCAS
Traffic Collision Avoidance System; neither aircraft was equipped with this technology, which would have provided resolution advisories.
Primary Radar
The ATC system in use only provided 2D positioning, leaving the controller unaware that the Kazakh flight had descended below its assigned level.
Interesting Facts
- 01It remains the deadliest mid-air collision in aviation history.
- 02There were no survivors from either aircraft.
- 03The Kazakhstan crew struggled with English terminology, confusing 'maintain' with 'descend'.
- 04The Kazakh crew was accustomed to metric altitudes (meters) and had to manually convert ATC instructions given in feet, increasing the risk of error.
- 05Delhi airport used primary radar only, which showed position but not altitude.
- 06The tail of the Ilyushin sliced through the left wing and horizontal stabilizer of the Boeing 747.
Safety Actions & Advisories
TCAS Mandate
The Directorate General of Civil Aviation (DGCA) in India mandated that all aircraft flying in Indian airspace be equipped with TCAS.
Air Corridor Segregation
Authorities created separate air corridors for incoming and outgoing traffic to prevent head-on conflicts.
Radar Upgrades
Installation of Secondary Surveillance Radar (SSR) at major Indian airports to provide altitude data to controllers.
Known Controversies & Unanswered Questions
Blame Attribution Disputes
Reference ↗In the immediate aftermath, Kazakhstan Airlines officials disputed the findings, suggesting that the aircraft were flying in turbulence or that the Indian ATC provided incorrect instructions. However, the flight data recorders eventually confirmed the Kazakh aircraft had descended below its assigned altitude.
Location
ACCIDENT SITE · Coordinates taken from the wikidata coordinate.