Airlines Filled More Seats in April, but That Can't Continue Forever

(MoneyWatch)  April traffic numbers are in for the airline industry, and we don't see much of a change from the trends in previous months. We do, however, continue to see rising load factors. The question is, how long can this go on?

Many think that the load factor is a simple measurement of the percentage of seats that have butts in them, but it's not quite that simple. It's actually a measure of the number of seats with butts in them times the number of miles flown (revenue passenger miles) divided by the number of total seats times the number of miles flown (available seat miles). Still, the result is the same. It shows how full the airline is.

These days, load factors tend to hover around 80%. That may not sound like a lot, but it's a remarkable achievement. That means that flights during peak times are completely full and flights during other off peak times are still pretty full. The days of half empty flights are increasingly rare.

This is good for airlines because they're able to better match capacity with demand, but it also leaves little room for error. When a flight cancels or things go wrong, then the chance of being able to reaccommodate people in a timely manner goes down. That's why you hear a lot of horror stories in that regard.

But can it go much higher? I'd say it's unlikely. Allegiant has been over 90% for most months, but that's a different airline model. They fly infrequently with a leisure traveler base. Those people don't cancel plans as often and tend to book up in advance. For most airlines, 80% seems to be pushing the limit, but there's no question they'll keep trying to go higher if they can.

Here's the April roundup. These are year-over-year comparisons for April 2010 vs April 2009. ASMs are "Available Seat Miles" (a measure of total potential passenger capacity), RPMs are Revenue Passenger Miles (a measure of filled seats and revenue earned), and Load Factor measures the relationship between the two:

Airline	ASMs	RPMs	Load Factor
AirTran	6.1%	8.1%	+1.5 pts
Alaska*	0.8%	7.1%	+4.8 pts
Allegiant	14.2%	14.4%	+0.2 pts
American*	(2.1%)	(1.3%)	+0.7 pts
Continental	(3.2%)	(2.6%)	+0.6 pts
Delta	(4.1%)	(2.2%)	+1.6 pts
Frontier	94.0%	106.0%	+5.0 pts
JetBlue	6.1%	6.0%	-0.1 pts
Southwest	(2.9%)	(0.6%)	+1.8 pts
United	(1.2%)	0.6%	+1.5 pts
US Airways#	(2.6%)	(4.8%)	-1.9 pts

*Does not include regional operations #Only includes wholly-owned regional subsidiaries

Photo via Flickr user Daquella manera