To be more specific,I believe point 4 from the QRH NNC for 'Airspeed Unreliable' relates to a possible failure of 2 or more pitot inputs. It could be a case where you have been subjected to 2 or 3 contradicting sources of IAS. The third memory item to crosscheck the IAS or Mach displays in order to identify the spurious source will have proven fruitless. The most important thing of all is to assume control of the aircraft. In a climb or descent simply fly a pitch attitude and a thrust setting to resume level flight. I have witnessed this failure in the sim on numerous occasions. The potential for confusion and eventual loss of control is untold. Some similarities can be observed with the unfortunate Air France A330 accident a few years back.