Analysis of complex systems is itself so difficult as to be subject to errors in the certification process . Complex interactions between flight computers and ADIRU 's can lead to counter-intuitive behaviour for the crew in the event of a failure . In the case of Qantas Flight 72 , the captain switched the source of IR data from ADIRU1 to ADIRU3 following a failure of ADIRU1 ; however ADIRU1 continued to supply ADR data to the captain 's primary flight display . In addition , the master flight control computer ( PRIM1 ) was switched from PRIM1 to PRIM2 , then PRIM2 back to PRIM1 , thereby creating a situation of uncertainty for the crew who did not know which redundant systems they were relying upon
Qantas Flight 72
Qantas Flight 72
Air data inertial reference unit