For what it's worth:

“Quick, contact traffic control,” Cynthia urged.

"Better call ATC" [or "Better call Center"], Cynthia suggested.

Why is the female Cynthia and the guy Perez? As in the military, female pilots are often referred to and addressed by their last name, unless this is a romance novel or a script for a daytime drama (I'm serious), in which the female would indeed be referred to by her first name.

Perez flipped a switch.

Perez keyed the microphone.

“Cleveland Centre, LASS two niner seven eight heavy. Declaring Pan Pan Pan. Suspected explosive on board. Unable to land at Dulles,” Captain Perez said.

"Cleveland Center, LASS 2978."

"LASS 2978, Cleveland Center."

"Center, we're declaring an emergency. Apparently have an explosive on board. Need vectors towards an unpopulated area." [It's clunky to have all this s-p-e-l-l-i-n-g out the numbers, and do we have to have a nine in the number so the pilot can say "niner"? It's all unnecessary. If I were your editor, I would say change the flight number and put the number in as a number.]

“LASS two niner seven eight heavy, Cleveland Centre. Roger. Stand by.”

“We can head for the Allegheny National Forest, which should be about twenty minutes if we come right to 085,” Cynthia told Perez.

“LASS two niner seven eight heavy, Cleveland Centre. Do you have an aircraft handling situation?”
Delete this.

Captain Perez keyed the mic again. “Cleveland Centre, LASS 2978. We believe the device is nuclear, and we're gonna turn right to heading 085 and proceed towards the Allegheny Forest area. We want to minimize potential civilian casualties,” he announced.

“LASS 2978, Cleveland Center. Stand by.”

“What the hell is going on?” Captain Perez asked Cynthia as he started his right turn.

I don't know which way they're going, so I don't know whether 085 is to the left or right. I chose right. As noted above, if you have a bomb onboard that apparently you expect to detonate soon, you're going to tell ATC what you're doing, and they can/will clear the traffic for you.