The EPA’s Inspector General is investigating why the agency didn't get its specialized plane loaded with advanced sensors into the air over East Palestine until four days after the disastrous Norfolk Southern derailment last year.

The Associated Press reported on a whistleblower’s concerns this spring about the delays and discrepancies in the way the Environmental Protection Agency deployed its ASPECT plane that could have provided crucial information about the chemicals in the air and showed that tank cars filled with vinyl chloride weren't likely to explode as officials feared.

The notice the Inspector General quietly posted Tuesday about the investigation said the watchdog will look “to determine whether the EPA and its contractors followed ASPECT flight equipment deployment procedures during the East Palestine, Ohio train derailment" in the hope of improving the response to future emergencies.

The man who wrote the software and helped interpret the data from the advanced radiological and infrared sensors on the plane said this mission differed from any of the 180 other times this plane was used since the program began after the 9/11 terrorist attacks. Robert Kroutil said he is not sure why the ASPECT plane wasn't deployed sooner and why it only gathered limited information in two brief flights.

The EPA has defended the way it used the plane and said officials didn't even call for it to be deployed from its base in Texas until two days after the derailment despite the fact that the agency touts that the ASPECT plane can deploy within an hour of any kind of chemical disaster.

EPA spokesman Nick Conger said Wednesday that the agency will cooperate fully with the Inspector General's office.