Quite simply you cannot. It is widely stated you would need to be at a height of at least 40,000 ft to get even a hint of curvature if earth were round. Commercial aircraft are not allowed to fly this high. They are only allowed to fly just under this altitude. 36,000ft might be typical. In addition, the windows on commercial aircraft are small and heavily curved. Even if they flew high enough for a person to see curvature, it would still not be visible to passengers.
 179) If the Earth were constantly spinning Eastwards 1000mph then airplane flight durations going Eastwards vs. Westwards should be significantly different. If the average commercial airliner travels 500mph, it follows that Westbound equatorial flights should reach their destination at approximately thrice the speed as their Eastbound return flights. In reality, however, the differences in East/Westbound flight durations usually amount to a matter of minutes, and nothing near what would occur on a 1000mph spinning ball Earth.
The ancient Hebrew view of the earth was of a flat earth with a glass firmament that separated the “waters below” from the “waters above” (Gen. 1:6-7; Job 37:28), and in which the sun and moon were placed and had their daily circuit around and above the Flat earth (Gen. 1:14-18; Joshua 10:13; Job 22:14). The earth did not move and was set on a firm foundation, on pillars in the waters of the “deep”, a great ocean underneath the flat earth (Gen. 1:2; 1 Samuel 2:8; 1 Chronicles 16:30; Psalm 104:5; Proverbs 8:28-29). They did not believe in a spinning globe. If the false globe ideas were taught in ancient times, they were taught by the Babylonian Pagans, not God’s people.
The group had relocated to the United States by 1977, and it was there that they recorded their best-selling album, Breakfast in America. With more hit singles than their first five albums combined, it reached number three in the UK,[10] and top of the charts in America. The album is reckoned to have sold over 20 million copies since its release on 29 March 1979.[12]
19) Tycho Brahe famously argued against the heliocentric theory in his time, positing that if the Earth revolved around the Sun, the change in relative position of the stars after 6 months orbital motion could not fail to be seen. He argued that the stars should seem to separate as we approach and come together as we recede. In actual fact, however, after 190,000,000 miles of supposed orbit around the Sun, not a single inch of parallax can be detected in the stars, proving we have not moved at all.
Hodgson quit Supertramp in 1983. Davies's relationship with him had deteriorated[citation needed], and the group's last hit before his departure, "My Kind of Lady", featured little involvement from Hodgson as either a writer or performer. The song was a showcase for Davies's vocal range, with him singing in everything from a booming bass to a piercing falsetto to his natural raspy baritone. With Davies firmly at the helm, Supertramp returned to a more non-commercial, progressive rock-oriented approach with the album Brother Where You Bound and had another hit with "Cannonball". The band continued to tour and record for another five years before disbanding, with a mutual agreement between the members that Supertramp had run its course.[13]
34) Ship captains in navigating great distances at sea never need to factor the supposed curvature of the Earth into their calculations. Both Plane Sailing and Great Circle Sailing, the most popular navigation methods, use plane, not spherical trigonometry, making all mathematical calculations on the assumption that the Earth is perfectly flat. If the Earth were in fact a sphere, such an errant assumption would lead to constant glaring inaccuracies. Plane Sailing has worked perfectly fine in both theory and practice for thousands of years, however, and plane trigonometry has time and again proven more accurate than spherical trigonometry in determining distances across the oceans.

It is in evidence that, if a projectile be fired from a rapidly moving body in an opposite direction to that in which the body is going, it will fall short of the distance at which it would reach the ground if fired in the direction of motion. Now, since the Earth is said to move at the rate of nineteen miles in, a second of time, "from west to east," it would make all the difference imaginable if the gun were fired in an opposite direction. But, as, in practice, there is not the slightest difference, whichever way the thing may be done, we have a forcible overthrow of all fancies relative to the motion of the Earth, and a striking proof that the Earth is not a globe.

137) Another assumption and supposed proof of Earth’s shape, heliocentrists claim that lunar eclipses are caused by the shadow of the ball-Earth occulting the Moon. They claim the Sun, Earth, and Moon spheres perfectly align like three billiard balls in a row so that the Sun’s light casts the Earth’s shadow onto the Moon. Unfortunately for heliocentrists, this explanation is rendered completely invalid due to the fact that lunar eclipses have happened and continue to happen regularly when both the Sun and Moon are still visible together above the horizon! For the Sun’s light to be casting Earth’s shadow onto the Moon, the three bodies must be aligned in a straight 180 degree syzygy, but as early as the time of Pliny, there are records of lunar eclipses happening while both the Sun and Moon are visible in the sky. Therefore the eclipsor of the Moon cannot be the Earth/Earth’s shadow and some other explanation must be sought.

148) Quoting “Earth Not a Globe!” by Samuel Rowbotham, “It is found by observation that the stars come to the meridian about four minutes earlier every twenty-four hours than the sun, taking the solar time as the standard. This makes 120 minutes every thirty days, and twenty-four hours in the year. Hence all the constellations have passed before or in advance of the sun in that time. This is the simple fact as observed in nature, but the theory of rotundity and motion on axes and in an orbit has no place for it. Visible truth must be ignored, because this theory stands in the way, and prevents its votaries from understanding it.”
92) The Notre Dame Antwerp spire stands 403 feet high from the foot of the tower with Strasburg measuring 468 feet above sea level. With the aid of a telescope, ships can be distinguished on the horizon and captains declare they can see the cathedral spire from an amazing 150 miles away. If the Earth were a globe, however, at that distance the spire should be an entire mile, 5,280 feet below the horizon!
As previously mentioned, the reaction of bodies of water with sunlight is very different from that of land. Being largely transparent, light penetrates deeply into water, so that the sun’s light is absorbed throughout a thick layer from the surface to some depth rather than just on the surface, as with land. Additionally, water has a high specific heat, which means that its temperature increases very slowly as heat is added. Consequently, water exposed to sunlight does not change temperature appreciably throughout the day, so there is no heating of air in contact with the water. If anything, during summer afternoons, when land is rapidly heating, bodies of water frequently are cooler than air temperature. The cooler water chills the air in direct contact with it, so the air lying just above water often is cooler than air higher up. Since air temperature normally decreases with height, this temperature reversal from the norm is called a temperature inversion. Temperature inversions are common over bodies of water during late spring and into summer. Since this temperature structure is the reverse of what causes inferior mirages, inferior mirages are far less commonly noticed over water. This happens particularly during the summer, when inferior mirages are common over land.
Mr. J.M. Lockyer says: Because the Sun seems to rise in the east and set in the west, the Earth really spins in the opposite direction; that is, from west to east," Now, this is no better than though we were to say - Because a man seems to be coming up the street, the street really goes down to the man! And since true science would contain no such nonsense as this, it follows that the so-called science of theoretical astronomy is not true, and, we have another proof that the Earth is not a globe.

23.) If astronomical works be searched through and through, there will not be found a single instance of a bold, unhesitating, or manly ,statement respecting a proof of the Earth's " rotundity." Proctor speaks of "proofs which serve to show … that the Earth is not flat," and says that man "finds reason to think that the Earth is not flat," and speaks of certain matters being "explained by supposing" that the Earth is a, globe; and says that people have "assured themselves that it is a globe;" but he says, also, that there is a " most complete proof that the Earth is a globe:" just as though anything in the world could possibly be wanted but a proof – a proof that proves and settles the whole question. This, however, all the money in the United States Treasury would not buy; and, unless the astronomers are all so rich that they don't want the cash, it is a sterling proof that the Earth is not a globe.
124) Amateur balloon footage taken above the clouds has provided stunning visual proof that the Sun cannot be millions of miles away. In several shots you can see a clear hot-spot reflecting on the clouds directly below the Sun’s spotlight-like influence. If the Sun were actually millions of miles away such a small, localized hot-spot could not occur.