Planes being towed to maintenance
 

I heard one talking to LAX ground control as a flight # and then Alpha. such as flight 59alpha. I looked it up and thats not a flight #. what gives?

Same flight number was in operation either inbound or outbound so it designates the 2 different ones. If they were both 59 it would lead to confusion so 59 and 59a are assigned.

A consequence of "direct" flights that require a plane change?

If both segments are operating at the same time, that would mean that the passengers on the inbound segment are misconnecting to the outbound segment of their "direct" flight.:td:

Both. It could be Mongah Airlines flight 999 from Fresno to Sydney with a stop in LAX. Same flight number but the flight from Fresno is a CRJ and the outbound from LAX is a 747. CRJ in flight is Flt999 while the towed 747 is 999A.

You can also have two airborne flights of 999. If the CRJ from Fresno is late with the 3 connecting passengers but the other 250 people made the outbound from LAX and it left, the outbound from LAX would depart as 999A or the CRJ may be assigned 999A if it was delayed and left Fresno after the LAX outbound departure time.

Was this possibly an aircraft (Delta or another) using LAX Terminal 5? The protocol used by ground controllers when aircraft are being taxied between gates and hangars is to assign a call sign using the airport gate, with the word "tow" attached. Such as "United 68A tow" if Gate 68A is involved.

See this NTSB report summary where the issue arose: https://www.ntsb.gov/ntsb/brief.asp?...14X41599&key=1

I thought in this sort of situation they give the second flight to take off a very different flight number (like 9099 instead of 99) to avoid any potential confusion if they are in the same ATC zone.

i think so. I'll listen again tonight to see.