Although the ship is crashed at an angle, when the crew is inside the ship, it appears to be flat; i.e., the stairs and door are straight up and down.
The cutouts in the astronauts' seats which resemble human forms don't come close to being able to accommodate the astronauts' actual bodies, particularly their heads and arms.
Despite the ship crashing from presumably several miles up, there isn't a single wound or even a bruise visible on any of the astronaut's bodies.
After the three astronauts see their own bodies on the other ship, the "dead" Captain can be seen swallowing.
When Lt. Mason goes to take the ID card from his body double, the body double blinks.
When the ramp is lowering for the crew to exit the ship, the pneumatic/hydraulic poles supposedly lowering the ramp can be seen wobbling back and forth. This is especially evident when the ramp stops moving, but the poles can be seen moving loosely at the top.
The three astronauts look out of a porthole, but there is no glass to protect them.
When the ship is landing, the strings suspending it can be seen faintly.
Mason checks the atmosphere and concludes that the helmets are not needed, but when exploring an alien planet, the air that one breathes is not the only caveat. There also should be microbial life taken into account or even poisonous plants or ferocious animals, none for which he checked for.
The only equipment each of them carries to check the crashed ship is a flashlight. If humans evolved to undergo interplanetary exploration, it would make sense to have specialized equipment.
Throughout the beacon exploration (ever since Mason found the blip on the radar and up to landing on the planet) there seem to not be any protocols to be followed. The captain gives best-practice orders (especially regarding restraint for Mason) but doesn't invoke any procedures. For example, apart from not carrying any mission-specific equipment, all three leave to check the crashed ship and leave their own ship unmanned.