The Adventures of Tintin: The Secret of the Unicorn

See also: The Secret of the Unicorn Â§Â Synopsis
In 1955, journalist Tintin and his dog Snowy are browsing in an outdoor market in Brussels, Belgium. Tintin buys a miniature model of a ship, the Unicorn, but is then accosted by an Interpol officer named Barnaby and a dreaded gangster named Ivan Ivanovitch Sakharine, who both unsuccessfully try to buy the model from Tintin. Tintin takes the ship home, but it is accidentally broken in an incident with Snowy and a cat in his apartment, resulting in a parchment scroll slipping out of the model and rolling under a piece of furniture. Meanwhile, bumbling police detectives Thomson and Thompson are on the trail of a pickpocket, Aristides Silk.
After visiting Maritime Library, Tintin returns to finds that the Unicorn has been stolen. He visits Sakharine in Marlinspike Hall and accuses him of the theft. When he sees a miniature model of the Unicorn, he notices that Sakharine's model is not broken, realizing that there are two Unicorn models. Once Tintin returns home, Snowy shows him the scroll. Barnaby visits them in a second attempt to give him the Unicorn, but is assassinated. After reading an old message written on it, Tintin puts the scroll in his wallet, but it is stolen by Silk the next morning.
Tintin is abducted by accomplices of Sakharine and imprisoned on the SS Karaboudjan. He learns that Sakharine formed an alliance with the ship's staff and led a mutiny to take over control. On board, Tintin meets Captain Haddock, the ship's nominal captain. Haddock is permanently drunk and thus unaware of the happenings on board his ship. Tintin, Haddock, and Snowy eventually escape from the Karaboudjan in a lifeboat but the ship's crew tries to ram the lifeboat. This fails because they instead notice an empty lifeboat that the Captain accidentally released before the escape and ram it instead. Presuming them to have survived by the number of lifeboats, Sakharine sends a seaplane to find them, which the trio seize and use to fly towards the fictitious Moroccan port of Bagghar. However, the seaplane crashes in the desert, due to low fuel.
While trekking through the desert, Haddock hallucinates and remembers facts about an ancestor of his, Sir Francis Haddock, who was a 17th-century captain of the Unicorn. Sir Francis' treasure-laden ship was attacked by the crew of a pirate ship, led by Red Rackham and after his eventual surrender, Sir Francis sank the Unicorn, and most of the treasure, to prevent it from falling into Rackham's possession. It transpires that there were three Unicorn models, each containing a scroll; together, the scrolls can reveal coordinates of location of the sunken Unicorn and its treasure.
The third model is in Bagghar, possessed by Omar ben Salaad. Sakharine causes a distraction in a concert, that results in him successfully stealing the third scroll. After a chase through the city, he gains all the scrolls by having his men toss Captain Haddock and Snowy in the water to force Tintin to go after him instead of saving the scrolls. After the boat leaves, Tintin is ready to give up, but is persuaded by Haddock to continue. With help from officers Thompson and Thomson, Tintin and Haddock track Sakharine down, who is revealed to be a descendant of Red Rackham. They head back to port and set up a trap, but Sakharine uses his pistol to resist arrest. When his men fail to save him, Sakharine challenges Haddock to a final showdown. Sakharine and Haddock sword-duel with cranes and swords eventually resulting in Sakharine being defeated and pushed overboard the ship by Haddock. When climbing ashore, Sakharine is arrested by Thomson and Thompson. Guided by the three scrolls indicating the location of Marlinspike Hall, Tintin and Haddock find there some of the treasure and a clue to the Unicorn's location. Both men agree to continue their search of the shipwreck.

Question: Why does the seaplane crash into the desert?
Answer: low fuel