Ryanair B738 and B738 at Dublin on Mar 8th 2015, blocked transmission leads to loss of separation on runway
Last Update: December 25, 2015 / 20:08:11 GMT/Zulu time
Incident Facts
Date of incident
Mar 8, 2015
Classification
Report
Airline
Ryanair
Flight number
FR-8036
Departure
Cologne, Germany
Destination
Dublin, Ireland
Aircraft Registration
EI-DHA
Aircraft Type
Boeing 737-800
ICAO Type Designator
B738
A Ryanair Boeing 737-800, registration EI-EFF performing flight FR-342 (callsign RYR342) from Dublin (Ireland) to London Luton,EN (UK) with 179 passengers and 6 crew, was taxiing for departure.
The tower controller intended to release EI-EFF for takeoff before landing of EI-DHA and queried the crew, whether they were ready for departure upon reaching the hold short line, the crew replied in the affirmative, and tower demanded a "good taxi speed if possible", instructed the aircraft to hold short of the runway initially and advised landing traffic was on a six mile final.
When EI-EFF reached taxiway E1, landing traffic now at 3.5nm, tower queried whether they were ready for immediate rolling departure, the crew - not having received "cabin clear" - replied in the negative, tower however understood affirmate, turned off the stop bar lights and cleared the aircraft to line up runway 28 and for takeoff.
At the same time the crew received the "cabin clear", the crew therefore read back their takeoff clearance.
After completing the turn onto taxiway E1 EI-EFF reduced taxi speed to about 5 knots however. This unexpected slow down prompted the tower controller to re-assess his plan and separation and he instructed the aircraft to hold short. However, this transmission was blocked by another transmission (source remained unknown despite the investigation) and EI-EFF did not read back that transmission, tower also did not turn on the stop bar lights. After crossing the hold short line the crew queried to reconfirm their takeoff clearance, the controller affirmed and added the word "immediate".
Tower advised the arriving aircraft to expect a late landing clearance.
Air Traffic Control's Runway Incursion Monitoring and Conflict Alerting System (RIMCAS) activated issuing a conflict alert to the tower controller.
EI-EFF became airborne before EI-DHA touched down. The separation between the aircraft reduced to 807 meters/0.43nm at a low closure rate with the departing aircraft past taxiway E5 accelerating through 138 knots at that point and the arriving aircraft approaching taxiway E3 at 146 knots and decelerating.
On Dec 24th 2015 Ireland's AAIU released their final report into the serious incident without formal conclusions but basically just stating the facts.
However, the AAIU commented:
Good communications are essential to the safe and orderly flow of air traffic. With traffic levels building up at that particular time of the evening, increased coordination was necessary between the Air Movements Controller and the Approach Controller in order to identify gaps for departing traffic.
When EI-EFF came on the AMC’s frequency, the Flight Crew of EI-EFF confirmed that they would be ready on reaching the runway. Based on the length of time for taxi and present location, the Flight Crew reasonably anticipated they would be ready on reaching the runway. As a consequence, the AMC requested that a good taxi speed be maintained, if possible, with the departing aircraft being advised of the traffic on approach. The crew of EI-EFF could only be ready provided that they received a ‘cabin secure’ signal before take-off, which they had not received at that time. Making this known to the AMC would have provided the AMC with additional information and the sequence he was planning may have been revised accordingly.
With the departing aircraft on TWY E1, the AMC enquired if they were ready for an immediate rolling departure. The reply from the crew of EI-EFF was clipped and indistinct. Replay of the ATC recording confirms that the reply was ‘negative’ but was understood by the AMC as an ‘affirmative’ reply which would have been consistent with the reply he had heard earlier. While the negative reply to the enquiry was made, again it was not made clear to the AMC that the ‘cabin secure’ signal had not yet received and consequently it was not possible to depart expeditiously.
Although requested to keep a good taxi speed, the departing aircraft slowed to 5 kts following its turn onto TWY E1. This was not expected by the AMC and prompted him to re-consider his plan for the departure/arrival sequence, consequently he requested EI-EFF to hold short. However, this transmission from the AMC was crossed by a simultaneous transmission; the source of the simultaneous transmission could not be determined as no other aircraft or vehicle made a call subsequently. While in the process of reading back the clearance for an ‘immediate take-off’ the crew of EI-EFF received the ‘cabin secure’ chime. The option to illuminate the TWY E1 stop bar as the aircraft approached was not taken by the AMC.
In order to plan efficient and safe sequencing of arrivals and departures on a single runway operation, ATC need to be able to anticipate the ‘readiness state’ of aircraft taxiing for departure. However, ATC should be aware that it may be difficult for flight crews to know early in the taxi ‘if they will be ready on reaching’; as often the flight crew will not have received confirmation (intercom or chime) of the cabin being secured.
Subsequent to this incident, the IAA installed a ‘Time to Touchdown’ facility (TTT) for the Tower Controller (AMC) which displays the time to touchdown of the next aircraft on final approach. Associated Air Traffic Control procedures have been developed, safety assessed and implemented and the use of TTT should greatly reduce the risk of the event occurring in the future.
Aircraft Registration Data
Incident Facts
Date of incident
Mar 8, 2015
Classification
Report
Airline
Ryanair
Flight number
FR-8036
Departure
Cologne, Germany
Destination
Dublin, Ireland
Aircraft Registration
EI-DHA
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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