Yesterday I flew UA 936 ORD-IAD and throughout the flight ATC refered to us as UA8146 Heavy. Anyone know why?

"Heavy" is common parlance for 772's (UA936 was a 772) and 744's...refers to wake turbulence caused by the larger birds, IIRC

This is usually when another aircraft with the same flight number is still flying.

Edit: Are you referring to 8146 or heavy?

OT, but I was on 966 ORD-IAD yesterday

I understand the "heavy" designation...was just wondering about where 8146 came from.

A "heavy" aircraft is one capable of a maximum takeoff weight in excess of 255,000 pounds, regardless of its operating weight at the time. Examples would include the 747, 777, 767, 757-300, DC-10, L1011 and DC-8-71.

UA often uses different flight numbers with ATC on flights that continue or originate domestically but have an international segment. This is presumably due to the fact that in the event of a delay, you could have two fiights in the air at the same time with the same flight number, s situation that the ATC computers cannot handle. There was a thread about this somewhere, perhaps a search will turn it up.

Thanks very much...very informative. ^

I asked about this a while ago, and what us2 says is correct.

Also, on Friday a captain explained over the PA that he would be using a "radio alias" of flight 8XXX, so perhaps this is the technical term.

8146 would usually be the nose number of the aircraft. The fleet is 8xxx for a 747 and the other three numbers are used to identify a subfleet.

It can change fairly easily within the company to help designate different sub-fleets within a fleet. The most common change is during an interior upgrade/change in which the number of seats/galley/lavs changes. This is how the schedulers and many others know the difference between planes without having to look it up or trying to remember all of the changes as they come out of maintenance. There are other sub-fleet designators such as overwater 737's that used to have life rafts in some of the stow bins.

The number 8146 can also be a radio call sign used when the same flight number is in the air at the same time.

Hope that helps.

It's the airline that creates the aircrafts call sign, not ATC. As an air traffic controller for 23+ years, I wondered the same thing. More than once, I have seen two different aircraft in the ATC system with the same call sign. But we had to do some fancy foot work to make it work, since the system will NOT accept different aircraft with the same call sign. The reason for the same call sign is as you would expect. One flight is late. But the on going flight, out of the city, leaves on time.

I am sure there must be cases where the call sign was changed by the airline, to avoid duplication problems, and then I would not know about it. Yet, I have seen where it was not changed. Of course, the ATC automated data system rejects the second duplicate call sign, since, there can be only one "UAL123" flight. But since the flight is actually there, it would need to be fixed. So, I would fool the data system, by adjusting the call sign. In this case, I could change it to "UAL0123". And then all would be well, since it is not exactly the same call sign, by adding a zero! And it would still fit the character size limit of 7, for all aircraft call signs. And later on down the line, somewere else in the ATC system, no one would even know, or care, that we had to adjust the call sign, for the data to process. The call sign would still look and read correctly.

I think United often uses the 4 digit flight numbers for their own internal reasons. Ha,...I've said too much,...and no body cares....

Not true! Thanks a lot for sharing your experiences! ^ ^

When a flight (usually international) uses the same flight number but continues onward using a different aircraft, as is the case for UA936 (ORDIAD is a B777; whereas IADZRH is a B763), UA has a practice of using the nose number for the call sign on the domestic segment. This way, in case of a delay, they can dispatch the second segment without causing confusion to air traffic control. I guess they learn from experience.

Totally untrue...we all love insider stuff like this! Welcome to FT, thanks for keeping us from bumping into each other in the skies (in the bad way!) for 23 years, and by all means, keep the info coming!

This is not correct. They do not use the ship number, they have a fixed alias flight number. An example is UAL8146 referred to by the OP; it runs from ORD to IAD according to flightaware then continues to ZRH with a different aircraft that uses the flight 936 call sign.

http://flightaware.com/live/flight/UAL8146

Why they pick the numbers they do is a mystery; it seems to me that it would make more sense to use the prefix "8" followed by the marketed flight number. The 9900 and 9800 series of flight numbers are used for ferry and charter flights, but the 8800 and 8900 series are unused. In this case, the domestic segment of 936 would be 8936 instead of 8146. The other aspect of this is that they are not consistent in the use of these alias flight numbers; 888 is used on both the PEK-SFO segment and the SFO-LAX segment.

I stand corrected.

Looking at some of the details in FlightAware, perhaps the "8146" designation has something to do with the flight plan:

ROUTE: GIJ J146 WOOST J34 AIR J162 MGW JASEN4