Spicejet B738 and Indigo A320 at Delhi on Sep 2nd 2013, near collision, minimum separation 0 feet vertical and 300 feet horizontal

Last Update: December 1, 2015 / 17:39:35 GMT/Zulu time

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Incident Facts

Date of incident
Sep 2, 2013

Classification
Report

Cause
Near collision

Airline
Spicejet

Flight number
SG-234

Departure
Hyderabad, India

Destination
Delhi, India

Aircraft Registration
VT-SPJ

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Spicejet Boeing 737-800, registration VT-SPJ performing flight SG-234 from Hyderabad to Delhi (India) with 186 passengers and 6 crew, was on final approach to Delhi's runway 28.

An Indigo Airbus A320-200, registration VT-IEB performing flight 6E-286 from Delhi to Coimbatore (India) with 93 passengers and 6 crew, was preparing for departure and had requested increased separation from the previous departure, a Boeing 787-800, which was acknowledged by tower. Tower instructed the aircraft to line up runway 28 and wait nonetheless.

6E-286 was subsequently cleared for takeoff and was in its takeoff roll still firmly on the ground when SG-234 crossed the runway threshold at about 50 feet AGL and went around due to the still occupied runway and climbed out.

In the meantime 6E-286 rotated for takeoff and began its climb out, too. The separation between the two aircraft eroded, both crews received TCAS resolution advisories which were incorrectly interpreted and only partially followed, and the separation continued to erode.

A last second turn performed by the Spicejet B738 after acquiring visual contact with the Airbus avoided a collision, the minimum separation between the aircraft was 0 feet vertical and 300 feet horizontal.

After initially flying clear of conflict the aircraft again lost separation after resuming their climbs resulting in a second set of TCAS resolution advisories which were followed until clear of conflict. Both aircraft subsequently continued to their destinations for safe landing without further incidents.

India's DGCA released their final report concluding the probable cause of the serious incident was:

The Air Traffic Control made the initial error placing two aircraft in the conflict positioning and all opportunities that were available subsequently to block the progress of the error were not affected and the error was allowed to progress. The possibility of a machine related failure is ruled out and the Human Error attributable to different extent is seen manifested in all three work areas, ATC Tower and the Pilots in Both aircraft.

Following are the considered extents of Human Errors in their respective stations :

ATC Tower :

- Decision to Hold an aircraft on active runway which is to delay its take off till the wake turbulence conditions subside and in this time allowing the other to continue its approach for same runway thereby reducing their lateral separations.

- Inability to assess Conflict and thereby the risk in allowing the event to progress till the aircraft in approach executes the Go around from runway threshold point while the other is still occupying the runway and is about another 20 sec away in time before it rotated for take off un-sticking from the surface.

- Inability in exercising Judgment and decision to order rejection of the take off by the aircraft on the runway, an omission that allowed the take off aircraft to conflict in the take off path with another that has gone around from the same runway.

- No effective Air Traffic Control was exercised in the conflict situation with no transmissions to advise intruder traffic position or the instructions to resolve. The traffic conflict in this case are developed at altitudes in which the TCAS resolution advisories are kept inhibited and the Air Traffic Control has the major responsibility on conflict resolution.

- Air Traffic Control further failed in allowing traffic to progress adversely following the 1st traffic conflict resolution and thereby allowing another conflict TCAS RA event.

- Failure in exercising the effective Command Hierarchy system for situations where there are more then one controller on the station and are to handle Normal / Non Normal / Emergency situations.

- Hand over / take over procedure implementation as in para 3.1 C above

- In absence of any formal hand over / take over it is assumed that all three controllers named X,Y and Z are available on the channel. In emergency situation as in the present case the more experienced Controller (the instructor) should have contributed generating thereby the synergy in the system by effective resource management.

Indigo VT IEB :

- Recognizing that the aircraft in approach for same runway has just gone around discontinuing its approach, IEB should have rejected its take off and avoided thereby a traffic conflict situation in the take off path. VT-IEB was on runway at speed 82 knots when VT SPJ initiated the Go around and announced so.

- The progress of the intruder traffic in such conflict situation was not adequately monitored either by TCAS display or by other available means. This led to Vt IEB crossing over through the level of the intruder traffic VT SPJ with very low lateral Separations.

Spice Jet VT SPJ

- Failure to Preempt a developing situation (aircraft at position about 6 nm to touch down progressing in approach to land at speed about 160 knots and another aircraft on runway is going to take approx 2 more minutes before it initiated the take off roll which further lasts another 45 seconds before the runway is available)

- Aircraft continues its approach without the Landing Clearance and continues till the runway threshold, below the point marked as ‘Decision Height’

- Aircraft on its Go Around follows the expected Go around flight path till about 1600 feet radio height and then begins to descend for some time and climbs again. This maneuver is neither in compliance to Go around flight path or the commanded TCAS resolution advisories.

- The progress of the intruder traffic in such conflict situation was not adequately monitored either by TCAS display or by other available means. This resulted in aircraft maneuvers which converged the conflicting traffic instead of separations. (It is however acknowledged that the maneuver of right banking the aircraft after visually sighting the intruder aircraft in close proximity only saved this serious situation from a possible mid air collision accident).

The DGCA reported, that tower was staffed by three controllers at the time, an executive ATC (named Mr. X) was in charge of the frequency, a senior controller (named Mr. Y) was acting as instructor, and a trainee (Mr. Z) who was a fully qualified controller for Cochin and was undergoing training for Delhi.

The DGCA continued that it was expected the instructor would take over responsibility for the frequency from the duty controller and the trainee would then handle the frequency under his supervision. However, this procedure was not followed, the duty controller signed out of the logbook without the instructor formally signing in. In addition, the trainee was handling the frequency while the instructor was not wearing his headset and therefore "was offline".

The DGCA analysed: "By the laid down procedure on Handover / Takeover by the manual of Air Traffic services Airports Authority of India, it is expected that a mandatory 15 minutes overlap period is provided in which the relieved ATCO shall brief the relieving ATCO of Complete traffic situation. The relieving officer shall plug-in the headset and monitor the progress of the traffic. The relieving ATCO shall make a log entry of having received briefing and understood the traffic situation before assuming charge of Air Traffic Control duties. The procedure was not complied with in the present scenario."

The DGCA analysed that the instruction to line up runway 28 from taxiway C was issued when the arriving B738 was 8nm out at 2795 feet AGL, the departing Indigo crew had requested 3 minutes wait to have possible wake turbulence from the previous Boeing 787-800 arrival settle. The arriving Spicejet crew was advised to expect late landing clearance at short final.

About 1:40 minutes after the landing of the Boeing 787-800 the Indigo crew received takeoff clearance, still 80 seconds prior to their requested wait time. The arriving B738 was descending through 1482 feet AGL at that point.

When the arriving B378 descended through 275 feet AGL the departing Airbus commenced their takeoff roll.

When the A320 accelerated through 82 knots 22 seconds after beginning the takeoff roll the arriving Boeing crossed the runway threshold and went around reaching a minimum height of 29 feet AGL.

The DGCA wrote: "Controller Z (Trainee) at this stage seeing the conflict left the channel and the instructor who was still offline was also not in control. The Air Traffic Control was therefore unattended for few seconds till such time the controller X who had earlier handed over the channel took over again seeing the situation and passed instructions. He remained on channel till the conflict was over and subsequently handed over to the instructor again at 08:56:00. The take off of VT-IEB therefore continued and VT–IEB was unstuck to runway at 08: 53:05 and at this instance VT-SPJ having gone around was at 455 ft AGL and climbing. VT-SPJ was laterally positioned behind VT-IEB but was flying faster. VT-IEB was vertically below VT-SPJ but was climbing faster. The two traffic therefore were in conflict in the take off path and were converging both vertically and laterally."

The DGCA analysed that TCAS RAs were inhibited for the A320 climbing below the B738 however at a higher vertical speed still below 1100 feet AGL, hence the TCAS also could not issue a TCAS RA to descend to the Airbus. Instead, the B738 received a reversed TCAS RA "Descend! Descend Now!" after receiving an initial RA to climb, the crew levelled off and initiated a descent, which increased the closure rate however and the aircraft crossed. The A320 finally received a RA to climb, the RAs were increased to "Increase descent" (demanding -2500 fpm of rate of descent off the B738) and to "Increase Climb" to the A320 - the two aircraft were separated by 176 feet vertically and about 520 feet laterally at that point, both aircraft were now above 1475 feet AGL with all RAs available.

The B738 crew got sight of the A320 and rolled right to 30 degrees bank angle. The DGCA wrote: "A mid air collision is hence narrowly avoided."

The A320 is now above the B738, both crews received "Clear of Conflict" advisories from the TCAS, the A320 continues the climb. At about 3200 feet AGL the A320 reduce their climb to accelerate while the B738 continues their climb to safe altitude, a secondary conflict arises and another set of TCAS RAs is being generated, both aircraft fly clear of conflict adhering to the advisories.

Six safety recommendations were released as result of the investigation.
Incident Facts

Date of incident
Sep 2, 2013

Classification
Report

Cause
Near collision

Airline
Spicejet

Flight number
SG-234

Departure
Hyderabad, India

Destination
Delhi, India

Aircraft Registration
VT-SPJ

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

This article is published under license from Avherald.com. © of text by Avherald.com.
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