 In April 2007 , the NTSB made four further recommendations , three measures to avoid fatigue affecting the performance of air traffic controllers , and one to prevent controllers from carrying out non @-@ essential administrative tasks while aircraft are taxiing under their control . Although these recommendations were published during the course of the NTSB 's investigation into the accident to Comair Flight 5191 , they were in part prompted by four earlier accidents , and the Board was unable to determine whether fatigue contributed to the Comair accident . 
 In April 2007 , the NTSB made four further recommendations , three measures to avoid fatigue affecting the performance of air traffic controllers , and one to prevent controllers from carrying out non @-@ essential administrative tasks while aircraft are taxiing under their control . Although these recommendations <a href='uninflect' title='1'><mark>were</mark></a> published during the course of the NTSB <a href='null_genetive' title='2'><mark>'s</mark></a>investigation into the accident to Comair Flight 5191 , they <a href='uninflect' title='3'><mark>were</mark></a> in part prompted by four earlier accidents , and the Board was unable to determine whether fatigue contributed to the Comair accident . 
In April 2007 , the NTSB made four further recommendations , three measures to avoid fatigue affecting the performance of air traffic controllers , and one to prevent controllers from carrying outt non @-@ essential administrative tasks while aircraft r taxiing under their control . Although these recommendations was published during the course of the NTSB  investigation into da accident to Comair Flight 5191 , they was in part prompted by 4 earlier accidents , and the Board was unable to determine whether fatigue contributed to the Comair accident .