Widebody Transport
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Inflight Event / Encounter Weather / Turbulence
Flight Crew Overcame Equipment Problem; General Maintenance Action
Weather; Aircraft
Sometime on descent between FL290 and FL240; got numerous indications of pitot static icing; including IAS comparator alert on both PFDs. Airspeed on Captain's side indicated approximately 30 knots higher than FO (First Officer); and 20 knots higher than STBY. Autopilot and Autothrottles were inoperative. Ran QRH for AIRSPEED UNRELIABLE. On final approach at 2000 FT; all indications returned to normal. Landed uneventfully.My impression was that the pitot static anti-icing systems seemed unable to keep up with high demand of heavy rain and low temperature; even though no icing was evident on the windscreen. Maintenance record after our write-up indicates that debris was found in the RH and AUX Pitot Systems.Increase heating ability of pitot static system. I am sure pitot system inspections are normally adequate; but perhaps the interval for such inspections should be looked at.
On descent I noticed an airspeed comparator indication on PFD 2 and then PFD 1. I informed the Captain and picked up the QRH. At this time I noticed numerous level 2 alerts and level 1 alerts. The autopilot; auto throttle and flight director systems tripped off.I ran and complied with the Airspeed Unreliable checklist in the QRH. An uneventful landing was made. Icing up of the Pitot Static system.
Air Carrier flight crew reported IAS anomalies; probably due to pitot static icing.