Problems with animated object lifetime and transformation controls

resetMaxFile #noPrompt
(
	--Initialise arrays
	global frame	= #()
	global flight = #()
	global points = #()
 
	--Read in the movement data
	local theFile = openFile "C:\\flights.txt"
	while not eof theFile do (
		t = (readValue theFile as integer)
		f = (readValue theFile as string)
		append frame t
		append flight f
		p = Point3 (readValue theFile as float) (readValue theFile as float) (readValue theFile as float)
		append points p
	)
	close theFile
 
	-- Initialise unique plane data arrays
	global planes = #()
	global listlastpos = #()
	global listlastdir = #()
)
 
 
	--Animate objects
	animate on 
(	
	animationRange = interval 1 frame[frame.count]
	--Initialise row-counter 'k'
	k = 1
 
	for t in 1 to frame[frame.count] do
	(
		at time (t)
		(
			while t == frame[k] do --Undertake action in relevant frames only
			(
				-- Initialise new plane
				if appendIfUnique planes flight[k] then
					(
						--Create new object - WHY DO THEY ALL APPEAR AT FRAME 1?
						Plane length:2000 width:2000 pos:points[k] isSelected:on
						$Plane001.name = flight[k]
						append listlastpos points[k]
						append listlastdir 0
					)
 
				else -- Plane already exists
					(
						-- Move plane to new position
						execute ("select $" + flight[k] as string)
						$.pos = points[k]
 
						--Retreive data on last transformations
						id = findItem planes (flight[k] as string)
						lastpos = listlastpos[id]
						lastdir = listlastdir[id]
 
						--Calculate current direction vector
						dirVec = normalize(points[k] - lastpos)
 
						--Calculate intended rotation
						rot = atan (dirVec.y/dirVec.x)
						if dirVec.x < 0 and dirVec.y > 0 then rot = 180+rot
						if dirVec.x < 0 and dirVec.y < 0 then rot = -180+rot
 
						--Unapply last transformations and apply new ones
						rot_obj = eulerangles 0 0 -lastdir -- Undo direction
						rotate $ rot_obj
 
						rot_obj = eulerangles 0 0 rot -- New direction
						rotate $ rot_obj
						-- WHY DO SOME OF THE OBJECTS SPIN WHEN TURNING ANTI-CLOCKWISE?
 
						--Remember current position and rotation
						listlastpos[id] = points[k]
						listlastdir[id] = rot
					)
 
				--Kill old planes (how to make them disappear when they've stopped moving?
 
				k = k+1
			)
		)
	)
	print "done"
)