"It had seemed a good idea at the time." Napoleon considered them as an epitaph. A coffin would be warm and terrestrial, opposed to his location outside of a perfectly good airplane.
He'd seen his target escaping. Napoleon was loathe to lose 'Lazarus', which now appeared to be a rotating courier name. Only the improvised runway disguised his presence at takeoff. Illya would know the change in the rate of fuel burned.
And the maximum ceiling of this craft and his lungs. Napoleon feared he'd misjudged the relation between the two. Good thing he'd chained himself on before losing feeling.