Pope Francis leaves Monday on an 11-day trip to Southeast Asia and Oceania, the longest and among the most complicated of his tenure. It could be particularly challenging for Francis, 87, who has been using a wheelchair and battling health problems.

But the trip, which includes a stop in Indonesia — the world’s largest Muslim majority country — also signals he has no intention of slowing down his outreach to faraway Catholics.

Francis will visit four countries for a total of about 20,000 miles by plane. From Indonesia he goes to Papua New Guinea, then East Timor and Singapore, as he deepens his engagement with Asia, one of his priorities.

The trip will include more than 43 hours of air travel and meetings with local faithful, clergy and politicians in cities with tropical climates or high levels of pollution on the other side of the world from Rome.

“It’s a physical test,” said Massimo Faggioli, a professor of theology at Villanova University, “and a sign that this pontificate is far from being over.”

The pope chose four island nations as he extends his outreach to what he calls “the peripheries,” a term for overlooked, faraway places with small, minority or persecuted Catholic communities. The trip is also one of Francis’ boldest engagements with Asia, a fast-growing part of the world, which the pope has always regarded as a strategic objective.