[Broncazonk]

Williamson Murray in Strategy for Defeat - The Luftwaffe 1933-1945 writes in conclusion, (Conclusion, page 303):

"For fighters, the attrition of German pilots over the war was probably well into the 90th percentile. The statistic mentioned in the last chapter on the average length of service of line pilots (between eight and thirty days) is an indication of the fate awaiting those who flew fighters for the Luftwaffe. The statistics for bomber, night fighter, or ground attack pilots could not have been much better."

The 8 to 30 day number does not come with a timeframe however.

Bronc