Professional Pilot, June 2017

T ower broadcasts Golf Seven Two One ceiling is 100 and RVR 200 meters in heavy rain Landing traffic reports braking action is poor The pilots who had been jostled around in the thick cloud deck for the last 40 minutes looked at each other as they mentally prepared to deal with a Cat III landing on a relatively short and very wet runway As 100 ft came and went neither pilot noticed any difference in visibility as they transitioned from cloud to rain Finally at 50 ft they spotted the runway lighting through the rain Unfortunately they arrived during one of the strongest monsoons in city memory Water had almost completely covered the landing zone and many of the roads to and from the airport were submerged With thrusters at idle stop the pilots flared and landed in what they later described as a splash down As soon as their mains hit the spoilers activated and the copilot spun up the thrust reversers while the pilot concentrated on keeping the bizjet on the centerline and avoiding hydroplaning Together the crew got the jet stopped 36 PROFESSIONAL PILOT June 2017 with a few hundred feet to spare and they were glad when the FBO brought a covered golf cart right up to the base of the air stairs and met them at the door with a large umbrella Getting their boss downtown would be yet another challenge Moving into the summer in the Northern Hemisphere means any number of things depending on the location For most of us summer heralds the hot season when the Sun is most directly overhead and increased density altitudes make for long runway rolls and sluggish climb outs But for others it means the start of a several month long downpour called the monsoon The term monsoon is derived from an Arabic word mausim which literally means season In many tropical and subtropical places where it is warm all year round but where there are distinct wet and dry periods seasons are defined by rainfall instead of temperature In fact although we commonly think of a monsoon as a wet weather phenomenon most places with a wet monsoon also include a dry monsoon period as part of their annual climate behavior Monsoons describe a highly predictable seasonal shift in the regional circulation that enhances the rainfall pattern in certain areas In many places the monsoon provides most of the annual rainfall total and plays a significant role in the socioeconomic behavior of the region in the form of planting and harvest times festivals and an expectation that transportation may be disrupted due to flooding However a wet monsoon differs from a more general spate of rain showers largely by its causal mechanism A big sea breeze A monsoon circulation is very much like the sea breeze circulation that a pilot might see on a warm day along the coast only at a much grander scale In most monsoons the change in tilt of the Earth relative to the Sun results in the Sun being more directly overhead in the northern hemisphere during the months of April to September and over the southern hemisphere from October to March This geographic relocation preferentially distributes heat over the favored hemisphere producing 2 things The 1st is a shift in the inter tropical convergence zone ITCZ the belt around the tropics where continual solar heating warms the ocean and the air above it This produces buoyancy and a ubiquitous ring of thunderstorms as the warm and humid air rises It is called a convergence zone because as the air within it rises cooler air rushes in along the surface from both the northern and southern hemispheres When WX BRIEF Monsoons These regular weather makers pose challenges for bizav flight ops and are becoming stronger and more erratic By Karsten Shein Comm Inst Climate Scientist Top Hindu statue is nearly submerged by the engorged Ganges river at Uttarakhand India in late June 2013 A more variable climate over the past few decades has decreased the predictability of the Asian monsoons and increased the likelihood of both monsoon failures as well as extreme rainfall events L Residents wade through flooded streets in India Monsoon rains often disrupt transportation infrastructure