NAGPUR, NOV 6: The Advanced Jet Trainers (AJTs) that the Indian Air Force was contemplating to acquire in near future will be minus the American components, Chief of Air Staff, Air Chief Marshal A Y Tipnis said here today.``We don't want American components in AJTs simply to avoid the effects of U S sanctions'', Tipnis told a press conference.The negotiations on the AJTs deal was in its prime stage, he said and expressed hope that it would be finalised by the year-end. ``It will take roughtly two to three years for actual acquisition of the aircraft'', he said.The IAF will acquire about 70 aircraft initially, Tipnis stated. To a query over the inordinate delay in finalising the deal for AJTs purchase, Tipnis listed various factors involved.Mere purchase is not only on agenda but ground support facilities and spares and components for repairs and maintenance assume equal significannce, which the IAF is taking care of, he asserted.When his attention was drawn towards the graph of MIG 21 crashes showing an upward trend, Tipnis claimed these operational aircrft used for training, though are quite old (since 1963) but still have good airworthiness.He admited candidly that about 40 per cent of causes of MIG-21 crashes were due to human errors. However, he clarified that the pilots are imparted a high degree of training for a long duration to avoid any chance of accidents.Tipnis said the first batch of MIG 21 was included in the Air Force fleet wayback in 1963. Periodic inspection and aging tests are routinely conducted to keep the MIG 21 fit for flying, he said to a query.He cited two main reasons for aviation accidents in the country, poor visibility and bird hits. The thick screen of smoke from domestic chimneys from slums near the airports and from industrial units are causing great amount of hardship for the pilots to locate the airport bases while flying.Indian skies are the worst polluted ones, he said. Similarly bird hits are another major factor for accidents, he added.``I flew recently a MIG 21 aircraft to dispel the apprehensions in the minds of young traineee pilots about airworthiness of these training aircraft'', Tipnis asserted.Tipnis, who earlier inaugurated a Commanders' Conference of Headquarters Maintenance Command (HQMC), complimented HQMC for keeping an excellent maintenance record of all IAF transport and fighter planes, machines and equipments.