3. (12 points) One of Alabama Air\'s top competitive priorities is on-time arriv
ID: 342519 • Letter: 3
Question
3. (12 points) One of Alabama Air's top competitive priorities is on-time arrivals. The airline defines "on-time" to mean any arrival that is within 20 minutes of the scheduled time. The airlines' management has monitored the performance for the past 15 weeks. They checked a random sample of 100 flight arrivals each week for on-time performance. The table that follows contains the number of flights that did not meet Alabama Air's definition of on-time (this is a P chart, no need to draw the chart, only calculations).
Week 1 2 3 4 5 6 7 8 0 10 11 12 13 14 15
Late Flights 2 4 10 4 1 1 13 9 11 1 3 4 2 2 8
Using 2-sigma control limits, develop the appropriate control limits for the percentage of late flights.
Explanation / Answer
Total number of Late flights
= 2 + 4 + 10 + 4 + 1 + 1 + 13 + 9 + 11 +1 + 3 +4 + 2 + 2 + 8 = 75
Therefore , proportion of late flights
= pbar = Total number of late flight / ( 100 flights/ week x 15 weeks )
= 75 / ( 100 x 15)
= 75/1500
= 0.05
Given , sample size = n = 100 flights
Control limit for p chart using 2 sigma control limits :
Upper Control Limit ( UClp) = pbar + 2 x Square root ( pbar x ( 1 – pbar)/n)
= 0.05 + 2 x Square root ( 0.05 x 0.95 / 100)
= 0.05 + 2 x 0.0218
= 0.05 + 0.0436
= 0.0936
Lower Control Limit ( LCLp ) = pbar - 2 x Square root ( pbar x ( 1 – pbar)/n)
= 0.05 - 2 x Square root ( 0.05 x 0.95 / 100)
= 0.05 - 2 x 0.0218
= 0.05 - 0.0436
= 0.0064
Upper Control Limit = 0.0936
Lower Control Limit = 0.0064
Upper Control Limit = 0.0936
Lower Control Limit = 0.0064
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