Data flaws hinder the Department of Transportation's ability to understand and fix flight delays and cancellations, the agency's inspector general found.

Although the DOT has improved how it assesses flight delays since 2000, the IG released a report on Dec 18. showing more improvements can be made.

The Bureau of Transportation Statistics collects data on 76 percent of domestic flights, thought it lacks the remaining 24 percent because only certain carriers are required to report delays. BTS also failed to include the initial cause of delay in almost 40 percent of flights analyzed, according to the IG.

"Addressing these data problems would go far in giving key aviation stakeholders and the flying public a fuller understanding of air carrier flight delays and their causes," the IG suggested.

The IG also found that the average length of flight delays has not improved since 2000, despite the number of flight delays declining overall. For example, for flights delayed more than 15 minutes, the average length of the delays increased from 51 to 54 minutes. More inclusive data would help get to the root of this issue.

Airline scheduling continues to affect the delay rate around the country. Overscheduling and congestion remain a problem at eight major airports, including Atlanta, Boston and LaGuardia, especially during the busiest times, according to the IG.

The benchmarks also used by the Federal Aviation Administration to determine airport capacity have not been publicly updated since 2004. Updated benchmarks will help fix flight overscheduling and determine what infrastructure improvements can be made to better airports overall, the IG said.

Recommendations by the IG included implementing ways to improve the "completeness and reliability of aviation industry data collected." Planned actions for the recommendations are "responsive," according to the IG, and it considers the issues resolved pending completion.