Last week, my Foolish colleague Rich Smith opined that Boeing (NYSE:BA) could end production of its iconic 747 jumbo-jet by mid-2017. By then, the 747 family will be nearly half a century old, but the newest version (the 747-8) would have had a production run of just 6 years.

It's true that Boeing's order backlog for the 747 has dwindled to just 39 aircraft, as of the end of November. Moreover, Boeing only sold 2 747s during 2014, and both of those sales were offset by order cancellations. However, there is still a niche market where the 747 makes sense for airlines.

The long jumbo-jet slump

Both Boeing and Airbus have had trouble selling their respective jumbo-jets recently. Freight versions have sold poorly due to a glut of air freight capacity caused by a combination of sluggish demand and rising underbelly capacity on passenger planes.

Emirates is the only airline that has bought many jumbo-jets recently. Photo: Emirates

Meanwhile, demand for passenger jumbo-jets has been weak as they tend to be less fuel-efficient than twin-engine widebodies: especially state-of-the-art models like Boeing's 787 and Airbus' A350. Those smaller models also tend to produce higher unit revenue, because with fewer seats available, airlines can command higher fares.

While Boeing and Airbus have both had trouble selling jumbo-jets, Boeing has definitely gotten the short end of the stick. That's because Emirates -- the only airline that is genuinely bullish about jumbo-jets -- has so far opted for the A380, ordering 140 of the type.

There's still a (small) market here

Emirates' ongoing interest big jumbo-jets suggests that there is still a market for these planes, though it is definitely a small niche. Jumbo-jets' massive size can be an advantage in capacity-constrained airports where the only way to meet demand growth is by using larger planes.

Indeed, Emirates is increasingly running up against capacity constraints at its hub in Dubai. That's the main reason why it has ordered so many A380s, even though Airbus has refused to spend money on upgrading the plane with more fuel-efficient engines.

There are a handful of other crowded hub airports across the world, so other airlines could have the same rationale for ordering jumbo-jets like the 747-8 and A380.

747s are still valued by airlines that operate in crowded hub airports. Photo: The Motley Fool

London-Heathrow is one example of a tightly slot-constrained airport. It's virtually impossible to acquire slots there, so if British Airways wants to add capacity at its main hub, it needs to use bigger planes. In fact, it is the largest operator of the 747-400 -- a 1980s version of the Boeing flagship that is ripe for retirement in the next few years.

British Airways is replacing some of its 747s with A380s and others with smaller but more fuel-efficient A350-1000s. However, there are still quite a few for which British Airways has not made replacement plans. The 777-9X -- Boeing's "jumbo-jet killer" -- should be ready by 2020 and could be a good option. But if British Airways wants something bigger than that, though not quite as massive as the A380, the 747-8 could be a good option.

New York's two international airports (JFK and Newark) face similar capacity constraints. At JFK, the crowding is especially bad in the late afternoon and early evening, when most flights to Europe depart. For airlines looking to add capacity, it may make more sense to use bigger planes like the 747-8 in those precious peak slots rather than adding flights during off-peak hours.

Oil prices will be key

Jumbo-jets like the 747-8 make more efficient use of gates, slots, and pilots than smaller widebodies. However, they tend to burn somewhat more fuel per seat, especially compared to next-generation models like the 787 and A350.

The future trajectory of oil prices will thus be key to Boeing's sales efforts for the 747. The jet fuel wholesale price has plummeted in recent months, and is now about 50% below the average level of the past 3 years.

US Gulf Coast Kerosene-Type Jet Fuel Spot Price Chart

US Gulf Coast Kerosene-Type Jet Fuel Spot Price, data by YCharts

If jet fuel prices remain below $2 and air travel demand remains relatively strong this year, a few airlines that operate in crowded hubs could take the 747-8 more seriously.

Given that the 747-8 production rate is down to 1.3 per month, Boeing only needs to sell a few dozen more to keep production going through the end of the decade. If oil prices remain depressed for any length of time, Boeing should be able to reach that milestone.