H25B, vicinity Kerry Ireland, 2015

H25B, vicinity Kerry Ireland, 2015


On 16 June 2015, the crew of a US-operated HS125 on a commercial air transport flight failed to continue climbing as cleared to FL200 after take off from Kerry for a transatlantic flight and instead levelled at 2000 feet on track towards higher terrain. Prompt ATC recognition of the situation and intervention to direct an immediate climb resolved the imminent CFIT risk. The Investigation found that the two pilots involved had, despite correct readback, interpreted their clearance to flight level two hundred as being to two thousand feet and then failed to seek clarification from ATC when they became confused.

Event Details
Event Type
Flight Conditions
Flight Details
Type of Flight
Public Transport (Passenger)
Flight Origin
Intended Destination
Take-off Commenced
Flight Airborne
Flight Completed
Phase of Flight
Location - Airport
Deficient Crew Knowledge-handling, Altimeter Setting Error
Vertical navigation error, IFR flight plan
Ineffective Monitoring, Ineffective Monitoring - PIC as PF
Accepted ATC Clearance not followed
Damage or injury
Non-aircraft damage
Non-occupant Casualties
Number of Non-occupant Fatalities
Number of Occupant Fatalities
Off Airport Landing
Causal Factor Group(s)
Aircraft Operation
Safety Recommendation(s)
Air Traffic Management
Investigation Type


On 16 June 2015, an HS 125-800 (N1310H) being operated by an unidentified US company on a commercial air transport flight from Kerry, Ireland to Gander, Newfoundland, Canada failed to follow its ATC clearance and reported being in level flight below the level of and heading towards surrounding terrain when in day IMC. ATC recognised the resultant imminent risk of CFIT and instructed the crew to commence an immediate climb. As a result, the flight, with 3 passengers on board, completed the reminder of its flight without further event.


An Investigation was carried out by the Irish AAIU after the occurrence was notified by Shannon ATC. It was based on ATC recorded data and interviews and a written report from the pilot.

It was noted that the 32 year old aircraft commander reported having 4,000 hours total flying experience which included 1,600 hours in type and that a Co-Pilot was also on board.

It was established that the aircraft had departed runway 26 at Kerry after one of the pilots onboard had correctly read back the ATC departure clearance "you’re cleared on track to VENER stop climb Flight Level Two Hundred squawk Six Three Zero Four". Soon after take off, the aircraft was instructed to contact Shannon and subsequently checked in advising "...Flight Level two zero zero direct VENER". Shannon then asked for a squawk and the passing altitude and received the reply "ah we are level Flight Level Two Zero Zero and squawking 6304”. The Shannon controller then confirmed radar contact and asked for confirmation of the passing altitude and received the response. "we were cleared only to Flight Level Two Zero Zero”. The Shannon controller persisted and transmitted “...that’s copied but your passing altitude...your current altitude” and this time received the response "...we confirm that we are cleared up to Flight Level Zero Two Zero… Two Thousand feet".

The exchange then continued with the Shannon controller transmitting "...negative climb Flight Level Three Zero Zero” which after correct read back was followed by Shannon transmitting "And November One Three One Zero Hotel, you can caution high ground…if you can expedite your climb till flight till correction …through Four Thousand feet” to which the response was “Expediting through up to Flight Level Three Zero Zero”.

Shannon subsequently asked the crew to confirm the Flight Level to which they had been cleared by Kerry prior to take off to which they received the response "we read back Flight Level Zero Two Zero… Two Thousand feet”. Shannon then advised that "Kerry seem to think that they gave you Flight Level Two Zero Zero" and that a report might have to be filed.

The Investigation was able to confirm that the climb to FL200 had been correctly given and read back using the ICAO standard form of flight level verbalisation (numbers only hence 'two zero zero') used in Ireland and included in ICAO Doc 9432. It was noted that this form of vertical clearance verbalisation was contrary to that advocated in the 2006 European Action Plan for Air Ground Communications Safety which states that "all numbers used in the transmission of altitude [,,,] which contain whole hundreds and whole thousands, shall be transmitted by pronouncing each digit in the number of hundreds or thousands followed by the word HUNDRED or THOUSAND as appropriate". This alternative procedure was noted as also consistent with the procedure introduced in the USA with effect from 3 April 2014. It is also being incorporated by EASA into the procedures to be included in the Standardised European Rules of the Air (SERA). However, after consideration of the available evidence, it was stated that "the Investigation does not believe that non-standard phraseology played a role in the Flight Crew’s misinterpretation of their cleared Flight Level".

The aircraft track and altitude after take off towards terrain exceeding 2000 feet QNH [reproduced from the Official Report]

The diagram above shows the aircraft level at 2000 feet heading towards the Slieve Mish Mountains which rise to 2800 feet and then the climb in response to the instruction from Shannon to expedite though 4000 feet. The aircraft commanders written report included "our altitude climb instruction was 'climb level Two Hundred' […] as we began to climb we had some confusion as to what the altitude clearance limit was as we were unsure what level Two Hundred meant (so) we levelled at Two Thousand feet to ensure we didn't exceed any altitude limits".

The fact that a previous investigation by the AAIU in relation to an event at Kerry had recommended to the IAA in 2010 that the provision of a radar display for ATC fed with existing ACC data had been made was noted. However, it was found that although this was being actioned (in conjunction with a similar plan for Knock Airport), progress had been very slow and there was still "no certainty around the timescale for completion of the project". Whilst it was considered that this facility would be of value in allowing Kerry ATC to monitor departures in the vicinity of high terrain in their area, it was accepted that "the lack of an operational ATM monitor in the tower at Kerry airport was not a factor" in the investigated event. There was, however, concern at both the slow ANSP progress in delivering a 'safety improvement' action relevant to the CFIT risk and the way in which the IAA had failed to track progress on a Safety Recommendation as required by Regulation (EU) No. 996/2010.

The formally-stated Conclusions of the Investigation included the following:

  • The aircraft levelled at Two Thousand Feet, contrary to its clearance.
  • Any confusion on the Flight Crew’s behalf did not originate from the non-standard phraseology.
  • In their written report after the event the Flight Crew indicated that they did not understand what Flight Level Two Hundred meant.
  • At no time did the Flight Crew seek clarification from ATC regarding their stop climb Flight Level.

The Probable Cause of the Serious Incident was determined as "the aircraft levelled at Two Thousand feet in close proximity to mountainous terrain, contrary to ATC clearance".

Two Contributory Factors were identified as follows:

  • The Flight Crew misinterpreted Flight Level Two Hundred as Two Thousand feet.
  • Clarification was not sought from ATC regarding the assigned stop climb Flight Level.

ATC Safety Action taken a result of the event was advised to the Investigation as the introduction of new procedures for non-standard IFR departures from Kerry. These include "Aircraft on Non-standard departures from runway 26 should be cleared to maintain the runway centreline until 4500 ft (to ensure terrain clearance) prior to commencing any turn […] departing IFR Aircraft on nonstandard climb outs should be requested to report an altitude at or above the applicable MSA prior to being handed over to the Shannon frequency".

Two Safety Recommendations were made as follows:

  • that the Irish Aviation Authority should expeditiously conclude all activities within its remit in relation to the introduction into service of air traffic monitors at Kerry and Knock (Ireland West) Airports. (IRLD2016002)
  • that the Irish Aviation Authority should review its procedures to monitor the progress of the action taken in response to Safety Recommendations received. (IRLD2016003)

The Final Report of the Investigation was published on 19 April 2016.

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