########################################################################################
#
# Load Factor: passenger-miles as a proportion of available seat-miles in percent
# Office of the Assistant Secretary for Research and Technology
# U.S. Department of Transportation
# http://www.transtats.bts.gov/
#
########################################################################################

american = read.table("american.txt",header=TRUE)
delta    = read.table("delta.txt",header=TRUE)
united   = read.table("united.txt",header=TRUE)

year = 2003:2014
ind = seq(4,nrow(data),by=12)


par(mfrow=c(1,1))
plot(american[,4],xlab="Month",ylab="Load factor",axes=FALSE,type="l",
       ylim=range(american[,4],delta[,4],united[,4]))
axis(2);box();axis(1,at=ind,lab=year)
title("International flights")
lines(delta[,4],col=2)
lines(united[,4],col=4)
legend(100,70,legend=c("American","Delta","United"),col=c(1,2,4),lty=1,bty="n")