Originally Posted by
lincolnjkc
What is actually wrong with the PMCO format? The last three digits match the fleet number, just ignore the first two digital as you would the UA suffix.
I have been curious about the historical reasons behind COs all numbers (I have suspicion is that Lorenzo and the ability to move aircraft between CO/EA/NY/PX/FL without giving away where they came from or having to rereg them may have some part on that) and the UA U the UA then back to U patterns.
IIRC there are some other airlines of the past (TW?) that used a purely numeric format for at least some of their aircraft so it's not limited to pmCO
CO used that format because the FAA bars the letter "O" from being used, due to the closeness with "0". CO could've done something like CA, CT, etc had they wanted to. TWA used TW on several aircraft. AA and DL use AA, AN, AM, DL, DN, DA, etc. UA could use UN, UT, or U or whatever. There's also some UA numbers that are free from aircraft long retired.
The issue with it is that the first two digits are almost never sequential. For the A321s, the first one is N44501. It would be somewhat easier if the next one was N44502. But that's not the case. The next delivered one is N14502. Then you have N24505, etc. Then some like 737 and 757s fleets overlap with the last 3 or 4 digits and it's a completely confusing mess. If they did something like N4501U or N4502C or N4503X or whatever, it would at least be a little easier. The first one or two digits being random and never sequential just makes the whole thing sloppy.