A spiral descent is made with the engine cut off, and the pilot should always keep his eyes on the centre of the circle. When the angle becomes too steep, he flattens her out a little so that he does not side-slip or skid, and if the descent is too rapid, he pulls the control lever back slightly. When the bank is too pronounced, the rudder and elevator change functions, and the pilot must bring them back to their proper positions at once. ZOOMING Zooming is really making an aeroplane suddenly jump several hundred feet into the air after flying near the ground. This is essential sometimes in order to clear a hangar or telegraph-pole near the ground. Fliers in the Great War did it when attacking aerodromes. No zoom, however, can be made unless the machine has got up full speed, for it is only this momentum that permits the aeroplane to climb so steeply and suddenly. The stunt is done by jerking the control lever back suddenly, which causes the nose to climb steeply. The control is then pushed forward equally as suddenly, just as the machine has reached the stalling-point and is about to fall over on its side. To avoid that, the control lever must be pushed forward, forcing the nose down, and allowing the machine to gain its velocity, otherwise it will lose its flying speed and crash. [Illustration: The so-called “Immelman turn.” The lower machine is turning on its back, while travelling forward, preparatory to diving.] LOOPING This stunt is nothing more or less than continuing the zoom until the machine flies upside down and completes a complete circle perpendicular to the ground. It is a very simple manœuvre, and was very necessary in aerial duels. Some machines were built so that they could loop easily. To loop, a machine must always get momentum enough in its descent to complete the circle. To start the loop, the control lever must be pulled far back, so that the nose rears vertically upward and over, and remains in an upside-down position for a few seconds. In this position he must cut off his engine, ease up the stick, slowly centring the control. The engine can be switched on again as soon as the steepness of the circle has decreased. Before looping, a machine should be carefully inspected because of the reversing of stresses, which may cause the breaking of a vital part. Another danger in looping is the stalling or stopping of the engine anywhere before the first half of the loop has been made, thus causing the aeroplane to fall over on its side and into a tail spin or spinning nose dive. NOSE DIVES