How to draw a heat blur from an aircraft engine
The heat blur effect is caused by the hot exhaust chaotically refracting the background. That is, the noisy turbulent hot air of the jet blast bends the light coming through it randomly, leading to blurry areas where the trail is. So to convincingly draw the heat blur you would need to have a background to be blurred.

That being said you could represent it by drawing the exhaust trail itself and slightly distorting the areas of the jet it overlaps. Since you are showing a heat trail and not a smoke trail you would want to go very light with the drawing in terms of tone and density. Try using fine lines and shapes that capture the jet trail's swirling movement.