Final answer:
The captain's indication of fuel on board as 8.7 likely represents 8,700 pounds of fuel, assuming the value is quoted in thousands of pounds and based on common United States conventions for reporting aircraft fuel.
Step-by-step explanation:
When the captain of an aircraft indicates his fuel on board as 8.7, he is generally referring to the remaining fuel in terms of thousands of pounds.
However, to provide an exact answer on what fuel weight this indicates, we would need to know the specific aircraft model's conventions for reporting fuel. In many cases, especially in the United States, fuel onboard is discussed in thousands of pounds, so the captain's indication of 8.7 would typically represent 8,700 pounds of fuel remaining.