Airline's obligation if mechanical problem
 

I understand that if a flight is cancelled due to weather, the airline is obligated to get you to your destination when possible on its own flights, but not obligated to use other airlines.

Is that also true if the cancellation is due to a mechanical problem? I thought I heard soemwhere that in this case, if another airline can accommodate you a full day sooner than the cancelling airline, you can insist on being put on the other airline.

Is that true?

I assume you are talking about US. Here is some information from Dept. of Transportation about passengers rights:

<i>Airlines don't guarantee their schedules, and you should realize this when planning your trip. There are many things that can-and often do-make it impossible for flights to arrive on time. Some of these problems, like bad weather, air traffic delays, and mechanical repairs, are hard to predict and beyond the airlines' control.</i>

and

<i>If you find a flight on another airline, ask the first airline to endorse your ticket to the new carrier; this could save you a fare increase. <b>Remember, however, that there is no rule requiring them to do this.</b></i>

Here is the webpage with more explanations:

<b>http://airconsumer.ost.dot.gov/publications/flyrights.htm#delayed</b>

This is all set out in the contract of carriage, which you should be able to look up.

In the one I have read, for US based flights, the airline will, at your request accomodate you on another airline, but only if the tariff is not higher on the other airline. And, of course, there are some other conditions, such as how long the delay will be.

I don't mean to blow you off, but in matters of contracts, it only makes sense to rely on the contract between you and the airline you are flying, rather than a generic response. Some of the contractual terms, of course, are based on regulatory requirements.

Thank you, I'll take a closer look at the contract.

My reason for asking was twofold:
first, I've encountered a few mechanical issues lately, but on domestic flights where other arrangements were available a few to several hours later;

second, I have a flight in a few days to the Caribbean where the airline only flies to the destination once per day - and the flights are pretty full - alternatives are limited.

Clevelandbrown is correct that the contract of carriage has your answer, but be careful. When you're looking at the contract of carriage for your upcoming trip to the Carribean, you'll need to look at the intl contract, which can be much denser and more difficult to get through. Most airlines have their contracts of carriage available on their websites but not all, especially the international one. If it's not there, you can go to the ticket counter at any airport and request a copy. They are required to provide it there per the government. Let us know what you find.