of transporting full pallets in the cargo hold, revolutionizing the air cargo industry. Modern air cargo Despite widespread hopes for a vibrant industry, for decades the air freight sector did not grow as expected and remained a very small part of total air traffic. For much of the first five post-war decades, most carriers saw it as a secondary activity, although there had always been specialized cargo airlines. Some passenger airlines have found the practice of carrying "belly cargo" to be a highly lucrative enterprise (in fact, it is estimated that 50% of all air freight is moved in this way), to the point where it has lessened the demand for dedicated large cargo aircraft. Cargo emerged as a solid pillar of the industry in the 1990s. The catalysts for the renewed growth in the sector were the express parcel carriers, typified by FedEx, DHL, PostNL, and UPS, and changes in practices in the manufacturing sector. In 1992, FedEx sent software on computer disks to thousands of customers, allowing them to track shipments from their own workstations. The rise of internet in the years that followed contributed to increase the reliability and accessibility to the air cargo industry. Most airlines now offer to their customers real-time flight status and the booking and tracking options. In addition, the industry is adopting electronic procedures, such as the electronic air waybill, to reduce the amount of paper documentation accompanying each shipment and increasing the security and safety of the transportation. Many retailers are making an effort to integrate the air cargo delivery process with their customer service offering to respond to increasing consumer pressure. An industry expert estimates that 15-20 tonnes of air cargo is worth 30-40 economy passenger seats, when both are on passenger planes. However, with the exception of the integrators (FedEx, UPS, DHL and TNT) the air cargo industry continues to suffer as the by-product 'poor-relation' of the passenger business. In 2017, the IATA observed a 9% rise in freight tonne kilometers: air cargo demand is strong due to industrial production and global trade growth above expansion of e-commerce, outpacing capacity as available tonne kilometers grew by 3%. Boeing doubled its 767F production since 2016 to three per month in 2020, and anticipates that total global air cargo traffic will more than double by 2041. See also History of aviation List of busiest airports by cargo traffic Antonov An-225, world's