Narrative:

On contact with departure control we were given altitude 'one four thousand' which the copilot repeated. Going through 5000 departure control said our clearance was to four thousand. The copilot told him our read back was 'one four thousand'. Departure said he missed it and was sorry and no problem now climb to nine.

Google
 

Original NASA ASRS Text

Title: ACR MLG ALT DEVIATION OVERSHOT DURING CLB OUT FROM PHL.

Narrative: ON CONTACT WITH DEP CTL WE WERE GIVEN ALT 'ONE FOUR THOUSAND' WHICH THE COPLT REPEATED. GOING THROUGH 5000 DEP CTL SAID OUR CLRNC WAS TO FOUR THOUSAND. THE COPLT TOLD HIM OUR READ BACK WAS 'ONE FOUR THOUSAND'. DEP SAID HE MISSED IT AND WAS SORRY AND NO PROB NOW CLB TO NINE.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.