There have been at least 140 instances where sensors on U.S. planes have been damaged by jetways, equipment on the ground, or birds in flight, according to a review of public databases by Bloomberg that extends back to the early ’90s. In at least 25 cases, damage to the “angle of attack” sensor, which is mounted on the fuselage near the nose of the plane, set off cockpit alerts or emergencies. The review—prompted by two Boeing 737 Max jets crashing in five months due to malfunctioning sensors meant to warn pilots when they near a perilous aerodynamic stalls—revealed the potential danger of counting on such devices. Boeing had also programed sensors on its best-selling Max model to automatically force the nose of the plane down, a decision now under scrutiny. “With that many pilot reports and with the unknowns that we’re dealing with in these two accidents, that’s an important area to be investigated,” said James Hall, the former chairman of the U.S. National Transportation Safety Board. The FAA was also aware the issues with failing sensors and said in a statement that it considers past incidents when it assesses aircraft design. “As part of the FAA’s oversight of the continuous operational safety of our nation’s aviation safety system, the agency continues to monitor, gather and evaluate all available information and data regarding the performance of aircraft and related components,” the agency said. The 737 Max has been grounded internationally since last month.