Horse boxes are only flown on freighters and combis. Look at the narrowbody luggage container and imagine fitting a standing horse inside.

I say fuel too . . . I was once on a flight with unusually strong head winds and they left everyone's luggage behind. . . but that was a regional turbo prop q400.

It wasn't horses - they don't fit standing up on a A320.
Bumping 15 passengers and their baggage would result in getting
about 5000 pounds more fuel onboard - the two engine ac would
burn that 5000 # in about an hour of flight.
Flights Eastbound generally have the aid of a tailwind.
Why the need for additional fuel - perhaps a mechanical condition
or a strange Weight/Balance situation ? Fueled boarded for W/B
haven't encountered that since the days of the 707-720B-DC8 !
Not likely that a maintenance part required in BOS would be ordered
from SLC - ATL is closer !
SLC granted a mountain altitude airport - but hot weather at this
time of the year - questionable - was the temperature 100 degrees ?
Critical cargo with a weight factor - why not FedEx ?
My guess would be a mechanical condition which would prevent the
aircraft from cruising at an energy efficient altitude requiring more
fuel to fly slower and lower or fuel for an enroute weather diversion.
How long did the flight take versus the scheduled flight time ?

Regarding that "PayLoad Optimized" - this is something that happens
with very long flights i.e. LAX-SYD - JNB-JFK - JNB-ATL when weather;
high priority premium cargo and full passenger loads are encountered
all requiring a maximum load of fuel. If after takeoff an event takes
place and the flight must return to the origin airport all that fuel has
to be ditched/dumped otherwise the aircraft will be too heavy to land
safely.

So I await the "Paul Harvey" - "The Rest of the Story"

If the flight crew used the phrase "payload optimized", it seems unlikely it was a mechanical or weather issue. IME, pilots tend to explain these, and the flight route on Flightaware doesn't really suggest weather as causing an atypical diversion. Payload optimized typically implies something cargo related... some sort of urgent equipment delivery that couldn't wait for the next Fedex perhaps?

"Fuel" by itself isn't an explanation, unless the airport ran out of it. Something was causing the airline to not be able to make its scheduled route within its maximum fuel capacity.

Delta Dash would be my guess. I've had manufacturing equipment shipped at great expense on Delta Dash. When I collected one particular item at CAE I was told that 12 people were asked to volunteer.

It was a large palatalized piece that had to go into a CRJ700. That 26k shipping bill was fun to give to the customer.

Thats what I was thinking also... Delta Dash got a time-critical equipment shipment that they took for some big bucks. Would have to be pretty large and heavy to require so many pax and cargo to get pulled however.

I don't see fuel as being an issue, especially on the SLC-BOS route which typically has good tailwinds. They fly the same equip on BOS-SLC into the wind without pulling off pax and luggage.

http://www.deltacargo.com/ProductsRa...DashHeavy.aspx
?

I have been on flights where people had to get off for cargo. The last time was in the middle of the South Pacific. Airlines would rather fly cargo than people. Cargo comes pre packed, do not demand upgrades, blankets, peanuts, or window seats.

That said I too am curious what the cargo might have been. Could have been space craft as USU builds satellites but not sure why it would head to Boston. Could have been other aviation parts but here again not sure it would head to Boston.

Hot, dry and altitude all limit aircraft performance. I remember afternoon flights from LAS in August (>110° at 2,200' with single digit humidity) where all of the luggage and some of the pax was bumped.

In this case SLC didn't have any WX to cause takeoff performance issues.

I asked about the weather in post #2. Later in the summer when it's really hot, this can become a big issue at high altitude airports, including SLC.

Going on the assumption that this was Sunday's flight, a quick check of the archived METARs shows that the temperature at KSLC at the time of departure was 33C(92F). That's easily enough to to start limiting takeoff performance numbers like RATOW or more likely Climb Limit at a high altitude airport.

The other end of the equation comes at BOS where the weather for the past 3 days throughout the northeast has been rain, low clouds, thunderstorms, and drizzle. An alternate would have definitely been required. Your standard alternate is normally within 100-200nm of the destination. With the extensive poor weather throughout the area, it would have been tough to find a suitable alternate with the apropriate forecast that wasn't several hundred miles if not further away. Since you must carry enough fuel to fly to destination and thence to your furthest alternate, that likely entailed the need for thousands of extra pounds of fuel (and may have even challenged structural landing weights).

Payload optimization is something tha gets designated by the dispatcher early inthe flight planning process whenever planned weights start approaching structural or performance limits. The designation gives both Load Planners and Gate Agents a set of protocols to follow. While it's more common on Intnl flights, it happens in the domestic world as well whenever Hot temps, high airports, and bad weather get involved. The combination of rising afternoon temps at SLC with the increasing fuel requirements of distant alternates likely caused a fluid situation right up to departure time

If (revenue) passengers who don't volunteer are removed from the flight, do they get IDB comp? My guess would be yes because I believe that only small aircraft get the weight and balance exemption from having to pay IDB.

Also, I would assume that the protocol does not involve giving people an explicit choice of flying without their checked bags or not flying at all on the flight, right? They just learn of the checked bag left behind when they go to baggage claim at the destination. Does DL do anything more than delivering the bag the next day?

What an interesting situation. Hoping someone has some definitive information, but I would think it had to be cargo of some sort. The route is indeed a little longer than is typical, but we are talking about an aircraft with a conservative range of ~3,300 miles on a flight plan of ~2,300 miles. The conditions do not seem extreme enough to warrant such drastic weight reduction.

This statement is not correct. No transport rated airplane on earth can carry the cargo bins full, every seat full, and the fuel tanks full. An A320 (and A319) can hold 42,000lbs of fuel in both wings and the center tank, and an A320 at 'normal' cruise/temperature/load/etc burns about 3,500lbs per hour. So the limiting factor is either max structural takeoff weight or max landing weight, because we all know an A320 can't blast off full and then fly for 12 hours. The exceedingly circuitous routing, combined with weather all over the northeast last night, probably necessitated an alternate landing field, which increased the fuel. The offload of all baggage, and then a few more passengers at departure time, makes me think the weight & balance planner was down to measuring the dirt on the airplane to get a few more pounds of performance.

But the "gold bars?" comment did make me smile.