Free transfer between airports in same city

A traveller recently asked and subsequently answered a question regarding transfer between PVG and SHA airports in Shanghai on China Eastern. The airline apparently does provide a voucher for free transfer if asked. This seemed surprising since nobody could find this information on the airline's web site.

Wikipedia provides a list of Metropolitan area airport codes of which the most well known ones are:

NYC: JFK LGA EWR
LON: LHR LGW LCY STN LTN SEN
PAR: CDG ORY LBG BVA
TYO: NRT HND

When an airline sells a ticket that requires transport between airports, this can in many cases be expensive.

I found two explicit cases where an airline publishes a policy for free ground transport:

Delta Airlines includes the following in their International Conditions of Carriage:

RULE 30 GROUND TRANSFER SERVICE

Delta or Delta Connection passengers making connections between LaGuardia Airport (LGA) or Newark International Airport (EWR) and John F. Kennedy International Airport (JFK) to or from Delta transatlantic flights will be provided ground transportation between JFK airport and LGA/EWR airports at no additional charge

GOL publishes the following on their website for Sao Paolo:

The free shuttle service GOL provides is subject to availability
...
To use the shuttle service between GOL airports, show the driver your boarding pass (in print or on a mobile device) or the receipt for your ticket purchase, along with your ID.

Delta Air Lines and AirFrance/KLM passengers can also use the shuttle for the CGH-GRU-CGH route by showing the driver their boarding pass or ticket purchase receipt, along with an ID.

Question: How is it possible to generally find out whether an airline provides free transport between airports co-located in the same city? e.g. are there any other examples of airline provided free transport in Terms and Conditions, Conditions of Carriage, or Fare Rules such that the wording could more easily be searched for when looking at other airlines? Or is the only option to ask the airline themselves at the airport?

Best Answer

There really isn't a general rule to availability of such transfers but airlines seem to reserve the right to provide it if they deem it fit to do so.

For example:

United's Rule 17:

Rule 17 Ground Transfer Service

UA may provide or procure ground transfer service between airports and city centers, between airports and any point in a Passenger’s itinerary, or to places of lodging.

Except where ground transfer service is directly operated by UA, it is agreed that any such service is performed by independent operators. Such independent operators are not agents or servants of UA, and UA assumes no responsibility for the ground transfer of any passenger and/or his/her baggage. Anything done by an employee, agent or representative of UA in assisting the Passenger to make arrangements for such independent ground transfer service shall in no way make UA liable for the acts or omissions of such independent operator.

In cases where UA maintains and directly operates local transfer services for its Passengers, the terms, conditions, rules and regulations of UA, including but not limited to, those stated or to which reference is made in UA’s Tickets, Baggage Checks and baggage valuation agreements shall be deemed applicable to such local ground transfer services. No portion of the air transportation fare shall be refundable in the event local ground services are not used by the Passenger.

While USAir/AA provide no such mention at all for either "Online" or "Interline transfers".

Southwest states explicitly that it would be at their discretion on whether or not to provide it:

c. Ground Transportation

(1) Unless provided at the direction of Carrier, Carrier does not assume responsibility for the ground transportation of any Passenger or his Baggage between any airport used by Carrier and any other location. Ground Transportation is at the Passenger’s expense.

So you would need to check with individual carriers that you fly in places where multi-airport connections are possible.