Civil aviation in India traces its beginnings to 18 February 1911, when Henri Pequet, a French aviator, carried 6,500 pieces of mail on a Humber biplane from Allahabad to Naini.[197] Later on 15 October 1932, J.R.D. Tata flew a consignment of mail from Karachi to Juhu Airport. His airline later became Air India and was the first Asian airline to cross the Atlantic Ocean as well as first Asian airline to fly jets.[198]

Investment in real estate can also be a source of a second income. If you have a decent sum of money lying around, you can use it to invest it to buy your second home. You may even take a home loan to finance your second home. This can become a source of income for you when you rent it to someone. These monthly rents would become your secondary monthly income. The key to making more money with rental properties lies in buying smart. Not all kind of property is going to give you a good return. Hence, analyzing the potential real estate opportunities is very important. The monthly rent highly depends on the area/location of the property hence it is highly important that you select the location of your property very wisely, keeping in mind the rent factor. You can save much even after your home loan EMIs. In addition to this, you can also avail tax exemption on the purchase of your property if it is through a home loan.

Income inequality refers to the extent to which income is distributed in an uneven manner. It can be measured by various methods, including the Lorenz curve and the Gini coefficient. Economists generally agree that certain amounts of inequality are necessary and desirable but that excessive inequality leads to efficiency problems and social injustice.[3]
While some people tend to use a savings account at the same bank where they have their checking account, make sure it's a high-interest one, not just a convenient one. "For short-term savings that you have parked in a savings account for easy access, you can often make more money just by researching whether you're getting the best interest rate," Goudreau says. "While many traditional banks offer as little as 0.1% interest on savings, online banks tend to offer higher interest rates. By switching to an account that offers 1% interest or more, you would be making 10 times as much just by moving the money."

Or, there is another theory for your primary salary – generate enough to have a little excess cash flow, but do it at a place that you can work stress free and have time to dabble in other projects.  A good friend of mine has this setup – he works 10-5 and makes $50,000 a year.  This allows him to easily cover all of his expenses, but the shorter hours and flexibility in his job allows him to pursue his secondary income generating ideas!
2. Focus on income-producing assets. Internet growth stocks may be sexy, but they provide no income. To build a large enough passive-income stream to survive, you must invest in dividend-generating stocks, certificates of deposit, municipal bonds, government Treasury bonds, corporate bonds, and real estate. You're free to invest in non-income-producing assets for capital appreciation too. You just want to earn reliable income when the day comes to leave your job.
The reverse can also be expected unless the rents rise too.  This rental increase might occur if we imagine interest rates are rising because the economic environment is improving.  At present, it is widely expected that rates will rise ever so slowly over many years.  Indeed the US has been looking for the courage to do this over recent months and they may start rising there soon.