CHICAGO (CBS) — A plane full of supplies for victims of Hurricane Maria was headed from Chicago to Puerto Rico on Tuesday; the same plane will bring back storm victims when it returns.

Another flight made the same trip on Monday, delivering 75,000 pounds of supplies, and bringing back more than 300 evacuees.

Only one United Airlines plane can make the roundtrip flight from Chicago to San Juan per day, so the airline was using one of the largest planes in its fleet to deliver the most supplies possible to Puerto Rico.

Workers were loading the Boeing 777 with food and supplies at O’Hare International Airport early Tuesday.

The mission is two-fold: deliver food and supplies to Puerto Rico, and bring back people stranded on the storm-ravaged island.

The entire island lost power after Maria slammed Puerto Rico last week. At least 85 percent of the power lines were knocked out and it might be months before they are repaired. Without power, pumps can’t bring running water to homes.

Maria also knocked out cell phone and internet service for most of the island; and food, fuel, and clean water are running short.

Monday night, more than 300 people evacuated from Puerto Rico landed at O’Hare, where volunteers from the Red Cross welcomed them with food, water, baby supplies, and clothes.

Families reunited and evacuees shared harrowing stories of being trapped and isolated after Maria devastated Puerto Rico.

“It’s a miracle, because we were actually going to wait for a week to get on a plane,” Frank Higginbotham said.

Tuesday’s relief flight took off around 6 a.m., and will return from Puerto Rico in the evening.