List six sub-headings to summarise the content of the six paragraphs below about the history of aviation.

Aeroplanes were once made of cotton, metal and wood, but many things have changed since

then. Aeroplanes improved once military and army work was found for them, which really

began in 1914. The aircraft improved in structure because the plane had to be able to carry

heavy weapons.

During the 1930s and the Second World War it was possible for planes to be bigger and

to fly faster, farther and higher, as well as to carry heavier loads. Advances in aerodynamics

helped engineers design ways to cut through the air smoothly.

As planes flew higher, pilots and passengers had increased difficulty breathing in the thin

air at high altitudes, so pressurised cabins were invented, which made breathing easier at

30,000 feet. In addition, improved radio equipment allowed pilots to receive flight directions

from the ground. Automatic pilots also came into use during the 1930s. These devices made

more accurate navigation possible and helped pilots avoid becoming tired on long flights.

All the major advances in aeroplane designs in the 1930s went into building the Douglas

DC-3. This twin-engine transport plane made its first passenger flights in 1936. It could

accommodate 21 passengers and could fly smoothly at 170 mph. It soon became the main

transport plane of the world's major airlines.

In 1958, Pan America World Airway began the first regular jet service between New York

City and Paris using the American Boeing 707 jet. This was a popular airline, which made it

possible for people other than the military to travel by air.

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