A brawl has broken out between United Airlines and Delta Air Lines over the run to Cape Town. United is going year-round into Cape Town from June, and Delta wants to start flying to the South African city later this year. Now United wants to add extra flights into Cape Town, and it's fair to say Delta is not happy about it.

Earlier this month, United applied for an extra allocation of three weekly US-South Africa frequencies to provide thrice-times-weekly, year-round flights between Washington DC (IAD) and Cape Town (CPT). The airline is already allowed to fly three times a week between New York Newark (EWR) and Cape Town - those flights beginning in June.

The additional Washington DC flights would start later in the year and use 257 seat Boeing 787-9 Dreamliners. United argues the flights will provide passengers extra choice, but the application remains up in the air - subject to approval from US and South African aviation authorities.

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Become an airline employee and your opportunities to travel and see more of the world can increase. Photo: United Airlines

"Delta's application is superior to United's in all material respects"

As part of the approvals process, US authorities call for submissions from potentially impacted parties. Step up Delta Air Lines. Delta's plans revolve around thrice-weekly flights from November between Atlanta (ATL) and Cape Town using 306 seat Airbus A350-900 aircraft.

"The Department should deny the authority sought in United's application or, alternatively, promptly move to institute a proceeding to weigh the merits of United's application against Delta's application to provide nonstop service to Cape Town, South Africa from Atlanta. Delta's application is superior to United's in all material respects," said the Atlanta-based airline in a March 18 Department of Transportation filing.

"The substantive merits of Delta's application and the public benefits that will flow from its proposal are so clearly superior to United's that the Department would be well justified in granting Delta's application now based on the relevant filings to date."

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Delta says their proposed Cape Town services are superior to United's planned flights. Photo: Delta Air Lines

Fight for the remaining allowed frequencies

Both airlines already fly to Johannesburg's O.R. Tambo International Airport (JNB), but flights to Cape Town have proved a tougher nut to crack. In a perfect world (at least from Delta's perspective), their South Africa flights would operate as US-Johannesburg-Cape Town-US triangle service. While US aviation authorities are okay with this, South Africa's aviation authorities are less keen.

The existing bilateral air services agreement between the two countries allows for 21 frequencies a week by US carriers. Delta argues United already has a "structural advantage."

"The net effect of United's proposal would be to give United a lopsided 5:2 advantage in weekly US - Cape Town flights and a 12:9 advantage in US - South Africa flights overall," argues Delta's submission. "This outcome if far from equitable and would only perpetuate United's current advantage on US - South Africa nonstop routes. In contrast, Delta's proposal, if granted, would equitably allow Delta to keep pace with United's US - South Africa frequency portfolio."

Here's the crux of the matter: only four of the 21 allowed frequencies are free. Both airlines fly daily to JNB, taking up 14 frequencies, plus United already has approval for the three times weekly CPT flights from Newark. Twenty-one minus 14 minus three equals four.

United's proposed additional three weekly flights to Cape Town and Delta's planned three flights a week add up to six - so there's a problem. As a possible solution, United proposes splitting the remaining four frequencies, something Delta isn't so keen on.

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There could be up to three nonstop routes between the US and Cape Town by the end of the year. Image: gcmap.com

Delta pushes for resolution

Delta's pitch to US authorities revolves around choice for passengers and providing a bit of pushback against United's dominance across the broader US - Africa nonstop market. Plus, there are a few cheap shots across United's bow - such as how much better the A350-900 is compared to the 787-9, and how flying through Delta's Atlanta hub is superior to flying through United's Washington DC hub.

"The math is simple: United has been awarded ten frequencies for South Africa service, Delta only seven," says Delta's submission. "Approving Delta's application enhances competition, and thus consumer benefits, whereas approving either of United's proposals would perpetuate an imbalance in South Africa flying or result in a United monopoly in serving Cape Town nonstop from the US."

Ideally, Delta would like the Department of Transportation to say no to United and award the frequencies to Delta to kickstart its Cape Town flights later this year. A less desirable alternative for Delta is splitting the available frequencies - and if the DOT wants to do that, Delta would like an answer pronto. The worst-case scenario is the Department of Transportation prefers the United proposal - effectively sinking Delta's planned Cape Town flights.