Originally Posted by
Bitterroot
Depends on how you do the math. From date withdrawn from revenue service to date returned to revenue service, it is, indeed, 38 days. (Nineteen total completed during 2011; two out at any given time; that calculates to 38.4 days per frame).
Recent examples: N769UA -- last service prior shopping at PEK was 29 November 2011; return to active service was 11 January 2012. That equals 43 days, which is six weeks; N219UA -- last service prior reconfiguration was 14 November; return to service was 26 December. That equals 41 days; another six week case. Yada yada.
You may be thinking more about the actual time individual frames are on the shop floor. That, however, does not accurately measure the calendar time that's typically required to go through the entire routine. There are some aircraft (N774UA and N775UA for example) that have gotten in and out in three weeks. Not most.
The other factor that affects the math is lags between one aircraft exiting reconfiguration and the next one going in. If there's time lost between the finish of one and the start of the next on the same line, that time is included in the 38 days. The actual time on the floor might be 30 days, but that's not the calendar time that drives when the entire fleet will be finished -- which was the underlying question.
Your math is faulty. Time out of revenue service does not equal time in modification. If UA was to do one airplane in 30 days and then take a 60 day break your math would say the average airplane takes 90 days. That is the wrong way to look at it as it provides a faulty idea of how long the work actually takes to complete one airplane.
N769UA did not start until December 1st, again, that messes up your math. N219UA was the prototype installation of the new Nitrogen Generating System which displaces oxygen in the fuel tanks with nitrogen enriched air. Including that airplane in your average once again makes you numbers off.
2/3 of the airplanes are being done in SFO, with an average time of 21-22 days. That means most of the fleet will be done in three weeks, not 38.4 days. The rest are done along with heavy maintenance in an average of 30 days.