loss of airspeed indication is not an emergency at cruise altitudes
In an Airworthiness Directive (AD) effective January 14, 2013 (2012-24-08) on the B737, the FAA maintains that the loss of speed information is a risk "catastrophic" that could cause the aircraft go of the flight envelope "we Are Issuing this AD to prevent prevention ice from forming on air data system sensors and therefore loss of airspeed indication or misleading airspeed indicating indication on all systems, who could lead to loss of control of the airplane. "
It is interesting to read in this AD the FAA's response to Boeing that has the same arguments as EASA and Airbus, "if pilots follow the procedure it's going well": Boeing Stated That loss of, or erroneous, airspeed indications do not Necessarily lead to loss of control Because --other indications Can Be Safely used to fly the airplane. Boeing Noted That in multiple events-have service without loss of control Occurred When The flight crew procedures Followed That Mitigate the loss of air data.
FAA Response: whether or not a procedure does not change, the loss of speed information is a catastrophic risk. We disagree / ... / ALTHOUGH Some In-Service events might-have Occurred without loss of control, loss of, or misleading airspeed indication is all airspeed indicating indication systems can, in fact, lead to an unsafe conditions of loss of airplane control. FAA Advisory Circular (AC) 25-11A, dated June 21, 2007 Typically classified loss of all airspeed displays (Including the standby display) as a '' catastrophic 'failure condition.