A NASA spokesman, David Mould, said Monday that the purpose of the study was “to develop methodologies” for analyzing data, not to find what the data would show. But Mr. Mould said the data from the questionnaires would be turned over to an airline pilots’ union and to a partnership between the airlines and the F.A.A., possibly by year’s end.  The deputy associate administrator for aviation safety at the F.A.A., Peggy Gilligan, said her agency had been briefed on the survey results but had not examined the underlying data. But she cast doubt on its value, saying the answers were not sufficiently detailed to determine, for example, whether two pilots describing similar problems were in fact talking about the same event.  Ms. Gilligan and the agency’s acting administrator, Bobby Sturgell, said they did not know whether the NASA data in fact recorded higher rates than their agency did of events like planes coming too close on the runway surface or in the air.  The F.A.A. said some problems covered by the questionnaire were becoming less severe, as measured by its own data, which it characterized as more detailed and rigorous. The number of “runway incursions,” in which a plane, vehicle or even a person is on the wrong spot on a runway, is down, it said, and the number of times that planes aloft came too close together has also declined.  The agency is undertaking an urgent program, with the airports and the airlines, to reduce the risk of runway collision, and has been criticized by the National Transportation Safety Board for not developing a cockpit warning system to prevent runway collisions. It is speeding the deployment of a system that warns tower controllers.  The Associated Press had sought the NASA survey data under the Freedom of Information Act. The news agency reported Monday that in a letter refusing the request, NASA said release of the data “could materially affect the public confidence in, and the commercial welfare of, the air carriers and general aviation companies whose pilots participated in the survey.”  The F.A.A. has long struggled with what to say publicly about the safety of individual airports or airlines. The agency was established in part to promote aviation, but in 1996, Congress decided that this job was in conflict with its role as a regulator, and removed promotion from its mission.  NASA’s mission includes helping to sustain the United States’ pre-eminence in aviation.  On Friday, Representative Brad Miller, Democrat of North Carolina and chairman of the Investigations and Oversight Subcommittee of the House Committee on Science and Technology, wrote in a letter to the NASA administrator, Michael Griffin, that possible damage to the image of the airline industry “does not appear to fall within any of the exceptions” to the Freedom of Information law, and that not releasing the information would be contrary to NASA’s mission of improving the safety and efficiency of airplanes.  Protecting airlines from public concern about safety, Mr. Miller said, was not part of the agency’s mission.  A version of this article appears in print on , on Page A23 of the New York edition with the headline: NASA Faces House Hearings on Air Safety. Order Reprints| Today's Paper|Subscribe
A House committee said it would hold hearings into why the agency is withholding 24,000 responses to a government-sponsored safety survey.