One of the differences between the TEGA on Phoenix and that on [Mars Polar Lander] was a thin retracting cover to keep the instruments from being contaminated by any stowaway microbes from Earth. [TEGA instrument head Bill] Boynton and his team had noticed, on a test version of TEGA, that the brackets at the bottom of this cover were just a hair's width too big, and as a result obstructed the doors. They sent revised designs for the cover to the manufacturer, Honeybee Robotics of New York. New parts were delivered and installed. But Honeybee had made the new parts using the original flawed designs -- and nobody in Tucson checked them. "They should've caught it and we should've caught it, but neither of us did," says Boynton, ruefully.
Honeybee Robotics did not make the design changes needed for the TEGA doors because drawings sent to the company from the University of Arizona were not clearly marked in this respect. A subsequent investigation by mission managers at the Jet Propulsion Laboratory found that Honeybee was not at fault.