B757 flight crew reported loss of captain's air data computer on takeoff roll. After liftoff they ra...

Narrative:

On the takeoff roll at 100 KTS I noted the captain's airspeed hung up while the first officer's was increasing. We took off and shortly afterward got an airspeed unreliable EICAS with a mach trim EICAS and rudder ratio EICAS. We told tower to keep us with them since we would be returning to the field for landing. After getting to initial altitude and after completing the after takeoff checklist I compared all three [airspeed indicators] and the first officer and standby [airspeed indicators] matched while the captain's [airspeed] was off at least 30-40 KTS. I sent an ACARS message to dispatch to call me and started the airspeed unreliable QRH checklist. When I received dispatch's frequency I had no luck contacting him on either radio. I asked for another frequency and he gave me [another] one and I also had no luck with either radio for that frequency. In the meantime we declared an emergency and had [approach] give us vectors; so we could finish the checklists. I completed the airspeed unreliable checklist and went to altn air data on the captain's side and all three airspeeds now matched up. We got the ATIS and landing performance and I also did the mach trim QRH as well as the rudder ratio QRH. Since my radio contact with dispatch never worked I sent him an ACARS message telling him we had declared an emergency because of unreliable airspeed and were returning to [departure airport] and to notify the company. Shortly after takeoff I informed the purser that we would be returning and to please give the passengers that information and that I would talk to them further when I was finished running all of the required checklists. After all of the irregular checklists were done as well as the approach descent checklist I gave the passengers an update on our return and information about the nature of our emergency. We had a light fuel load and made a normal weight landing with no further problems.

Original NASA ASRS Text

Title: B757 flight crew reported loss of Captain's air data computer on takeoff roll. After liftoff they ran the procedures; declared an emergency; and returned to departure airport.

Narrative: On the takeoff roll at 100 KTS I noted the Captain's airspeed hung up while the First Officer's was increasing. We took off and shortly afterward got an Airspeed Unreliable EICAS with a Mach Trim EICAS and Rudder Ratio EICAS. We told Tower to keep us with them since we would be returning to the field for landing. After getting to initial altitude and after completing the After Takeoff Checklist I compared all three [airspeed indicators] and the First Officer and standby [airspeed indicators] matched while the Captain's [airspeed] was off at least 30-40 KTS. I sent an ACARS message to Dispatch to call me and started the Airspeed Unreliable QRH checklist. When I received Dispatch's frequency I had no luck contacting him on either radio. I asked for another frequency and he gave me [another] one and I also had no luck with either radio for that frequency. In the meantime we declared an emergency and had [Approach] give us vectors; so we could finish the checklists. I completed the Airspeed Unreliable checklist and went to ALTN Air Data on the Captain's side and all three airspeeds now matched up. We got the ATIS and landing performance and I also did the Mach Trim QRH as well as the Rudder Ratio QRH. Since my radio contact with Dispatch never worked I sent him an ACARS message telling him we had declared an emergency because of unreliable airspeed and were returning to [departure airport] and to notify the Company. Shortly after takeoff I informed the purser that we would be returning and to please give the passengers that information and that I would talk to them further when I was finished running all of the required checklists. After all of the irregular checklists were done as well as the Approach Descent Checklist I gave the passengers an update on our return and information about the nature of our emergency. We had a light fuel load and made a normal weight landing with no further problems.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1081592
Time
Date	201304
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Takeoff
Flight Plan	IFR
Component
Aircraft Component	Air Data Computer
Person 1
Function	Captain Pilot Not Flying
Experience	Flight Crew Last 90 Days 220 Flight Crew Total 20000 Flight Crew Type 6600
Person 2
Function	Pilot Flying First Officer
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

B757 flight crew reported loss of captain's air data computer on takeoff roll. After liftoff they ran the procedures; declared an emergency; and returned to departure airport.