The failure of control-tower equipment at OR Tambo International Airport left dozens of planes grounded and thousands of passengers frustrated yesterday. The problems slowed international and local arrivals and departures at Africa's busiest airport to a snail's pace.Airline companies warned that there would be a huge knock-on effect on flights leaving and arriving in Johannesburg.The radio technology problems arose as South Africa's leading civil aviation safety and security experts met in Johannesburg for a safety and security conference yesterday.The meeting - during which it was revealed that aviation crashes and deaths had decreased - follows two deadly aircraft crashes in Limpopo and North West this week. The second occurred yesterday when a helicopter crashed, allegedly after losing power. Two people were critically injured.The spokesman for Air Traffic and Navigation Services, Percy Morokane, confirmed the failure of radio equipment at OR Tambo.He said a technical malfunction had interrupted communication between air traffic controllers and crew on planes at the airport and in the surrounding airspace."The malfunction occurred on Monday night. Within 25 minutes the situation was recovered. All operations returned to normal."But, Morokane said, during a review of the malfunction yesterday it had became evident that further steps were required to prevent risks."To maintain the normally high safety standards, air traffic rates to and from the airport and the airspace were temporarily limited, while the technical risks were mitigated,'' he said.''Unfortunately, the result of these safety interventions were the delays that were experienced. We are normalising and restoring the situation."He declined to reveal the exact nature of the problem or the "risk mitigations"."We have implemented contingency procedures. At no stage have flights been in danger."The cause of the equipment failure was under investigation, Morokane said.Arthur Bradshaw, an air-traffic management system adviser and former head air-traffic controller, said: "Radio failures have been around for some time, which is why you have a main and standby system, along with an independent battery backup system. That's three systems that are meant to kick in if one or the other fails."But if all these systems have failed, a very good explanation needs to be given to the public, who have a right to know what happened and what the problems are," Bradshaw said.Passenger Toby Shapshak, whose kulula.com flight from Cape Town to Johannesburg was delayed by nearly two hours, said passenges had been told the delay was caused by industrial action."Shortly after we boarded the plane the pilot informed us that due to industrial action by air traffic control staff at OR Tambo International Airport our flight would be delayed. We were unable to disembark as the crew didn't know how long we would be stuck for."Kulula sent us an SMS apologising for the delays. We were not the only flight delayed. An aircraft from Angolan Airlines was also delayed, along with several others," Shapshak said.Morokane denied that air traffic controllers had embarked on industrial action.Ian Meaker, the commercial distribution executive manager at kulula.com, said 34 of its flights had been delayed because of the communication network system outages.There would be a knock-on effect for all flights and all airlines, he said."This will delay flights to Durban and Cape Town."SAA spokesman Tlali Tlali said the delays had affected two of its flights from Port Elizabeth and Cape Town."Most of our intercontinental flights depart in the evenings. We will consider other options if the impact results in significant delays," he said.FlySafair said landing restrictions were being experienced at OR Tambo, which was experiencing technical issues with communications equipment."As a result, the airport has placed a limit on the frequency with which aircraft are able to land."The company said there had been a two-hour delay of one of its flights from Cape Town.At the meeting of civil aviation safety and security experts, the director of the Civil Aviation Authority, Poppy Khoza, said that between April last year and March this year aircraft accidents had decreased by 17% from 144 the year before to 120. There had been no accidents involving commercial aircraft.She said the number of fatal accidents had dropped by 41% from 27 to 16, while the number of fatalities from accidents decreased from 41 to 26."As much as the statistics are encouraging, we believe there is still room for improvement, particularly in relation to recreational and general aviation activities."Linden Birns, managing director of Plane Talking, said though the CAA did a good job in maintaining aviation safety standards in South Africa, the authority faced huge challenges in terms of resources."The number of aircraft registered in South Africa has more than trebled over the past 20 years, with the number of licensed pilots growing five-fold, a large number of these being recreational pilots."Birns said if the CAA was to be effective in its oversight tasks it had to be properly resourced...