Date: 201311
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: Turbulence; Icing; 0
Light: Daylight
Aircraft: Gulfstream IV / G350 / G450
Operator: Air Taxi
Operating under: Part 135
Flight plan: IFR
Mission: Ferry / Re-Positioning
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Pitot/Static Ice System
Component problem: Malfunctioning
Reporter organization: Air Taxi
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Human factors: Troubleshooting
Second reporter function: Pilot Flying; Captain
Anomaly: Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Aircraft Equipment Problem Dissipated; Flight Crew Took Evasive Action
Contributing factors: Human Factors; Weather; Aircraft
Primary problem: Aircraft

Narrative: While at 11;000 FT and 210 KTS; we noticed that our Number 1 AOA indication was going into the Amber (Caution) limit (.6). We compared the data with the Number 2 AOA; which was showing approximately .42 AOA. The Captain expressed concern to myself that he suspected the Number 1 probe was possibly showing inappropriate indications and that we should keep an eye on it. We were then instructed to descend and maintain 10;000 FT by ATC. Approximately 2 minutes later the Number 1 AOA probe went into the Red (Warning) limit (1.02) and the Number 1 stick shaker was activated with no pusher; loss of Autopilot; Flight Director; Navigation; Yaw Damper and EICAS messages; 'DADC MISCOMPARE;YAW DAMPER OFF' as well as other cautions and messages that were associated with the message. The Captain immediately applied power and started hand flying the aircraft when we noticed that the Number 1 airspeed indicator started to 'X' out and called for 'Flaps 10' to prepare for the possibility of a stall and to stabilize the aircraft; disengaged the autothrottles and applied manual thrust. After assessing the condition of the aircraft and current flight status; the Captain determined that the Number 1 AOA had iced over and that the Number 1 PFD was displaying incorrect data; and the Captain made the command to transfer the Flight Director and navigation to the Number 2 PFD; pulled the Number 1 CB to stop the stick shaker; and asked me to fly the aircraft until he could determine the cause of the bad information. At this time we received a radio call from ATC asking us to stop our descent; and the Captain replied appropriately to ATC that we would comply. At this time I started to compare altimeters between the Number 1 and Number 2 PFD's noticing that the altitudes were off by approximately 600 FT (9;400 FT MSL vs. 10;000 FT MSL) Approximately 10 seconds later we received another call from ATC instructing us to again stop our descent in which the Captain replied 'standby' due to the confusion of why ATC asked us to stop descending; when we were under the impression that we were maintaining level flight. ATC then responded 'NO; STOP YOUR DESCENT NOW' to which the Captain then asked me to climb because of the instructions coming from ATC. During this period GA thrust was applied and the aircraft was climbing and accelerating through 240 KTS and 10;600 MSL. Approximately 10 seconds later the aircraft was passing through 11;000 FT MSL when the Number 1 PFD information started to agree with the Number 2 and standby systems. At this time the Captain transferred control back to himself and reengaged the Yaw Damper; Flight Director; Heading Mode; autothrottles and re-engaged the autopilot. We also noticed that the Transponder Mode S control on the center console was tuned to the Number 1 ADC and concluded that ATC had asked us to stop descending due to the bad altimeter indications coming from the Number 1 Pitot Static system. At this moment I believe the aircraft was approximately 11;000 FT and 250 KTS with Flaps 10 extended configuration. After assessing the status of flight; the Captain immediately started a descent back to 10;000 FT and pulled the throttles to idle to slow the speed. Subsequently we also received a call from to ATC to maintain 210 KTS and to slow our speed. Passing through approximately 10;300 feet MSL we again received a DADC MISCOMPARE advisory message; as well as several Caution messages associated with the indication; in which we immediately concluded that the Number 1 system had again failed; selected the opposite DADC controller on the Display Controller; re-engaged the Yaw Damper; autopilot; autothrottle; and Navigation system in Heading Mode and continued to comply with ATC instructions. At approximately 5;600 FT MSL the MISCOMPARE advisory cleared and we were able to land uneventfully with no abnormal caution or advisory messages.


Second narrative: [Report narrative contained no additional information.]


Synopsis: G-IV flight crew experiences airspeed; altitude and AOA anomalies descending to 10;000 FT. This results in stick shaker activation; Mode C readout error along with autopilot; flight director and yaw damper EICAS messages. Eventually the Captain's PFD is transferred to the number two DADC and the stick shaker circuit breaker is pulled. A normal approach and landing ensues; with the number one DADC returning to normal passing 5;600 FT in VMC.