They said no damage was caused in the runway incident but such objects "have the potential to cause serious harm to aircraft".
Metal debris on a runway led to the Concorde crash in Paris in 2000 which killed 113 people.
The incident happened at 6:15pm on 7 August last year, involving a Loganair Embraer 145 jet with 35 passengers and three crew on board.
The towbar had been accidentally dropped on the runway some 30 minutes earlier by the solo pilot of a Cessna 210 light aircraft.
He had forgotten he had left it attached to the nose wheel of his plane and it fell off as he took off.
The UK Department for Transport's air accidents investigation branch (AAIB) said he may have been distracted by thinking about how he earlier nearly collided with a cyclist who had pulled out in front of him as he drove to the airport on his motorbike.
The report said as the Loganair plane's commander applied the brakes on landing, "he saw an object on the right of the centre line approximately 8-10m in front of the aircraft.
"He estimated the aircraft was travelling at between 105 and 110 knots (120-126 mph) at this stage.
"He applied slight left rudder as the object disappeared out of view and felt a small bump through the rudder pedals, but was not sure if this was caused by the aircraft clipping the object or running over the centre line."
The AAIB report said: "A general aviation towbar was inadvertently left attached to an aircraft because the pilot had been distracted by an earlier stressful event during his journey to the airport.
"The towbar dropped onto the runway during the departure and remained there for approximately 30 minutes, during which two other aircraft used the runway and a runway inspection was completed.
"A landing aircraft then ran over it.
"The towbar was inconspicuous because it did not have any reflective or other high visibility markings."
It recommended the Civil Aviation Authority "communicate to the general aviation community the importance of increasing the visibility of ground equipment".