Airlink Flight 8911 – The case for direct and seamless radiotelephony communication.
On 24th September 2009, Airlink flight 8911[1] crashed following engine failure after take-off. Once airborne, the aircraft climbed to 500 feet AMSL then lost altitude and made a forced landing on a small field 1.4 km from the end of the runway. An innocent bystander was struck by the wing of the aircraft and the three crew members were seriously injured. The captain subsequently died from his injuries.
The factual information from the accident report states in part as follows;
Another witness, an airline pilot, stated that his own aircraft was taxiing to the apron as the accident aircraft started rolling. According to this pilot, ZS-NRM became totally engulfed in smoke from the moment when it increased power (“not just smoke but THICK blue smoke”). The pilot added that as the aircraft rolled down the runway, it looked “like an airshow”, with smoke emanating from the right engine.He and his co-pilot were shocked, yet were reluctant to tell the crew of ZS-NRM to stop because they feared being blamed if the abort went wrong. Instead, they enquired of the tower whether the aircraft was aware of the smoke. By the time the ATC responded, ZS-NRM was already in the air, but with its landing gear still down. The pilot of another aircraft, waiting at the holding point, informed ZS-NRM that their undercarriage was still lowered. The captain of ZS-NRM then transmitted (instead of using the intercom) an instruction to his co-pilot to raise the gear. During this transmission, the sound of the fire-warning bell could be identified in the background. At that point, the airline pilot reported that he could no longer see ZS-NRM.”
The report further states;
The tower controller later stated that the aircraft was still on the runway and in the vicinity of the intersection with taxiway G when he became aware of smoke coming from it. He could not, however, make out exactly from which part of the aircraft the smoke was coming from.
Despite the smoke, no warnings were generated in the cockpit during the take-off roll and the fire-warning bell sounded when the plane was off the ground. The engine started smoking at the commencement of the take-off roll, yet the crew received notification during rotation when it was no longer possible to abort the take-off.
Hesitation, uncertainty, and delay to notify the crew of ZS-NRM formed part of the accident chain.
Would the outcome have been different if the pilot of the taxiing aircraft had notified the flight crew of ZS-NRM?
What is the role of Air Traffic Control in such a situation and what is the communication protocol?
Air Traffic Control Services are provided for the purpose of; preventing collisions between aircraft, preventing collisions with obstructions on the maneuvering area and to expedite and maintain an orderly flow of air traffic[2].
At controlled aerodromes, air traffic controllers[3] are responsible for coordinating all aerodrome traffic in a manner that ensures safe and expeditious aircraft movement
The controllers give information and issue instructions through radiotelephony exchanges on VHF radio frequencies.
These frequencies belong to the ground stations and only two-way air-ground communication[4] is permitted.
An exception to this rule is for vehicles that operate on the apron and in close proximity to runways[5]. These are authorized to use the VHF frequencies.[6] The rationale for using the same frequency is to enhance situational awareness as flight crew and vehicle drivers can listen in and monitor transmissions authorizing other vehicle or aircraft movements, which helps minimize runway incursions and possible collisions.
Even during technical failures or adverse and potentially hazardous weather conditions observed or visible to other flight or ground crews on the same frequency, this information should only be transmitted to air traffic control, who in turn communicate the same to the concerned crews.
Why is this so? From their vantage positions high above the aerodrome, controllers have a bird’s eye view of all operations and are in a good position to spot any externally visible malfunction on aircraft during taxi, takeoff/landing roll and during the initial climb/final approach.
In addition, tower controllers have access to updated weather information provided by the aerodrome meteorological office[7] and are in the best position to advise on parameters like surface wind, atmospheric pressure, visibility and cloud base.
On most occasions, controllers do a good job and this is reflected in a number of investigation reports where accurate and time-saving information has been passed on to flight crews.
In 1985, the flight crew of British Airtours Flight 28M abandoned their take-off believing the thud they heard during the take-off roll was a puncture or bird strike. Unknown to them, the number one engine had suffered an uncontained failure and punctured the wing fuel tank. An aural fire alert went off in the cockpit and the crew received confirmation of the same from the tower controller, who advised them to evacuate the aircraft from the starboard side.
In 2016, the flight crew of Korean Air Flight 2708 rejected their take-off following a fire breaking out in the number one engine. Although the crew already had knowledge of the fire and had started decelerating, the tower controller reported the fire to them, ordered them to stop on the runway and await the arrival of the fire trucks.
Unfortunately, controllers have limitations. They are not always able to spot every defect and furnish flight crews with timely and accurate information. Secondly, controllers do not screen or test the veracity of weather reports provided by the meteorological office.
Thirdly, controllers are not pilots and may not appreciate the significance or severity of certain events[8]. Lastly, controllers are human and are prone to making mistakes, either
The 1991 crash of Nigeria Airways Flight 2120 was caused by a blown-up tire during the take-off roll that caused a fire in the wheel well when the gear was retracted. According to eyewitnesses, sparks and smoke were visible during the take-off roll until the gear was retracted.
These sparks were not visible to the controller because the landing gear was partially obstructed by the fuselage, and being located 1100 meters from the runway threshold, the viewing distance would have prevented the controller from identifying a flat tire even if the line of sight had not been obstructed.
Incorrect wind figures provided by approach control was determined to be a contributing factor in the 1992 crash of Martinair Flight 495. The figures provided were for runway 29 yet the aircraft was vectored to approach and land on runway 11 at Faro Airport – Portugal.
The 2010 crash of Afriqiyah Airways Flight 8U771 was partly attributed to weather information issued by air traffic control and the ATIS[8].
This information was different from the prevailing conditions within the vicinity of the aerodrome. Runway 09 which was in use at Tripoli International Airport that morning was not ideal for the prevailing weather conditions and approach control should have instead vectored the aircraft to land on Runway 27.
The pilot of an aircraft that landed before the crash warned the accident crew and the tower controller of visibility and cloud base different[8] from what approach control had provided and that it was prudent to change the runway in use from 09 to 27.
It must be noted though that save for Nigerian Flight 2120 where the accident became inevitable upon retraction of the landing gear, crews involved in the other accidents failed to manage their aircraft according to procedures laid down in the different flight crew operation manuals. That failure ultimately led to the loss of control. However, this does not take away the fact that there was a contributory failure on part of air traffic control.
In the Airlink crash, hesitation, uncertainty, and delay led to a failure of one of the safety barriers. The barrier had two pilots on the taxiway and the controller. None of them acted in a timely manner due to fear of blame, uncertainty, and the existing radiotelephony protocol.
Just like pilots are permitted to depart from rules and established procedures in circumstances that render such departure absolutely necessary in the interests of safety[8], direct communications between crews should be permitted in emergency situations. This would allow for a seamless flow of information and shorten the time during which critical and life-saving decisions can be made.
High traffic density airports may be concerned with uncoordinated transmissions leading to frequency congestion during such emergencies, which may lead to other incidents. However, the air transport industry has set very high safety standards, making emergencies and accidents very rare[8].
Frequencies may be congested on rare occasions in the interest of saving lives and property. Flight or ground crews who pass on safety-critical information should neither be blamed nor punished for communicating life-saving information as blame and punishment have limited value as accident prevention tools. ZS-NRM could have rejected its take-off if the other pilots that observed the smoke trail had communicated this information to the accident aircraft in real-time.
The existing aviation radiotelephony protocol, although in place for good reason, partly explains why ZS-NRM crashed.
Unfortunately, the accident report did not make any recommendations regarding passing on real-time information to crews where technical defects have been observed by other flight or ground crews.
However, part of the knowledge gained from the crash of flight 8911 is that there is a need to reconsider changes to the aviation radiotelephony protocol. Direct and seamless communication is of significant importance when a defect or hazard has been identified and crews have to be urgently notified to give them the opportunity to make prudent decisions off the roll.
Sebina Muwanga
Air Transport Regulation Consultant
[1] Jetstream 4100, Registered ZS-NRM
[2] Annex 11 (Ch.1); Air Traffic Services.
[3] Divided into apron management and tower sections.
[4] Annex 10, Vol.2 (Ch.5); Aeronautical Communications.
[5] Tugs, fuel bowsers, runway inspection teams, bird hazard units, and RFF vehicles. RFF vehicles can communicate directly with flight crews on the ground during emergencies.
[6] ICAO Doc 9870 (Ch.4); Manual on the Prevention of Runway Incursions.
[7] Annex 3 (Ch.1); Meteorological Service for International Air Navigation.
[8] The controller’s uncertainty in the Airlink crash can only be attributed to a lack of knowledge of the significance of smoke being emitted from any part of the aircraft during the take-individually or as part of a team. These limitations are highlighted in a number of accident reports.