Date: 201306
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: MD-83
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Air Data Computer
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Troubleshooting; Workload
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew FLC complied w / Automation / Advisory; Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency
Contributing factors: Aircraft; Procedure
Primary problem: Aircraft

Narrative: Right at rotation Captain's airspeed indicator showing 15 knots slower than First Officer and STBY Airspeed Indicator along with FAST/SLOW fail lights both sides; unable to engage autothrottle; engine EPR power chevrons rolled back to 1.3 EPR on both sides; checked QRH checklist for CADC failure and while many indications did not match up it was the closest to our issue; tried CADC on 2 which resolved issue of Captain airspeed slow and also fixed chevron issue for power; so was able to re-engage AT. Due to lack of clarity of the issue and previous history of write-ups on this aircraft for related issues declared emergency and returned to the departure airport for overweight landing. Normal touchdown and rollout with weight at 137;500 approximately touchdown rate of 300 FPM; had Airfield Rescue and Fire Fighters follow us to gate after landing.


Second narrative: First Officer was pilot flying. On takeoff roll; Captain noted that his airspeed indication was approximately 15 KTS slower than the STBY and First Officer airspeed. After rotation; the First Officer's flight director and fast/slow indication became inoperative; the autothrottles disengaged; the Captain's fast/slow indication was inoperative; and the Captain's airspeed indication continued to be inaccurate. Talked to ATC; leveled off at 5;000 FT to troubleshoot. Ran the CADC Failure/Disagreement Checklist; but did not fix the problem completely; nor did switching the DFGS switch. The Captain's airspeed indicator did show correctly once switching to CADC 2. Since the indications we were seeing did not match up exactly with the QRH the Captain elected to return to the departure airport and not take the problem to another airport. We still had fast/slow flags and the IAS button on the flight guidance panel would not engage. The First Officer did get the flight director back and was able to engage the autopilot however. Captain declared an emergency for the overweight landing; briefed the flight attendants and passengers; and we returned uneventfully with a gentle touchdown of less than 300 FPM. Our brake temperature never rose above 100 degrees and was confirmed by Airfield Rescue and Firefighter (ARFF) and we taxied to the gate with ARFF following us.


Synopsis: After takeoff a MD-80 Captain's airspeed indicated fifteen knots slow; the First Officer's Flight Direct; Fast Slow indicator; and autothrottles were inoperative. After selecting the Captain to CADC 2; as per the QRH procedure; most systems functioned; but an emergency was declared and the flight returned to the departure airport.