C172 instructor pilot reported taking control of the aircraft and landing straight ahead shortly aft...

Narrative:

Was training a flight student and executing a soft-field takeoff on rnwy xy at ZZZ. During the initial takeoff roll; all indications were good. Air speed (as) indicator became 'alive' as the nose wheel came off the runway. Aircraft continued to accelerate and the mains came off the runway. The student initially 'over-rotated' causing the stall warning horn to very briefly alert. The student reduced pitch placing the aircraft back in ground effect. At this point; I looked at the as indicator and it [indicated] 30 knots. The ground speed appeared 'normal' and another glance at the as indicator showed less than 20 knots although we had not climbed. I quickly looked at the as indicator and the needle was now 'bouncing' between 0 and 50 knots very rapidly. I looked over the remaining available pavement which demonstrated several thousand feet of clear pavement. No obstructions and other traffic was clear of the landing path. I took the plane from the student and reduced throttle and landed the aircraft. Pre-flight [revealed] no obstructions of the pitot tube or static system. I determined it was safer to abort the takeoff than continue the flight.

Original NASA ASRS Text

Title: C172 Instructor Pilot reported taking control of the aircraft and landing straight ahead shortly after takeoff when he noted the airspeed indicator was malfunctioning.

Narrative: Was training a flight student and executing a Soft-Field takeoff on RNWY XY at ZZZ. During the initial takeoff roll; all indications were good. Air Speed (AS) indicator became 'alive' as the nose wheel came off the runway. Aircraft continued to accelerate and the mains came off the runway. The student initially 'over-rotated' causing the stall warning horn to very briefly alert. The student reduced pitch placing the aircraft back in ground effect. At this point; I looked at the AS indicator and it [indicated] 30 knots. The ground speed appeared 'normal' and another glance at the AS Indicator showed less than 20 knots although we had not climbed. I quickly looked at the AS indicator and the needle was now 'bouncing' between 0 and 50 knots very rapidly. I looked over the remaining available pavement which demonstrated several thousand feet of clear pavement. No obstructions and other traffic was clear of the landing path. I took the plane from the student and reduced throttle and landed the aircraft. Pre-flight [revealed] no obstructions of the pitot tube or static system. I determined it was safer to abort the takeoff than continue the flight.

Data retrieved from NASA's ASRS site 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	1401409
Time
Date	201610
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Takeoff
Component
Aircraft Component	Airspeed Indicator
Person 1
Function	Instructor Pilot Not Flying
Qualification	Flight Crew Commercial Flight Crew Flight Instructor
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Speed All Types

C172 instructor pilot reported taking control of the aircraft and landing straight ahead shortly after takeoff when he noted the airspeed indicator was malfunctioning.