Cockpit Weather Systems Risk: Flying in Close Proximity to Terrain Thunderstorms and Precipitation TAWS equipment is required for turbine‑powered airplanes  having six or more passenger seats and manufactured after  certain dates (see 14 CFR part 91, section 91.223). TAWS is  now an affordable option in many advanced avionics due to  decreased cost and increased capabilities of computer circuits  and components. All aircraft would be safer with TAWS and  crews trained to use the technology. fly based on the TAWS display. It requires much precision  flight training to learn the timing and skills to fly from a  display depicting a myriad of data and converting that data  into close and low terrain flight directions. All advanced  avionics are designed to help the pilot avoid a hazard, not  enable the pilot to get closer to it. TAWS is not a terrain  flight following system. Advanced avionics cockpit weather systems provide many  of the same weather products available on the ground and  have a variety of uses that can enhance awareness of weather  that may be encountered during almost any phase of flight.  Radar images, satellite weather pictures, Aviation Routine  Weather Reports (METARs), terminal weather forecasts  (TAFs), significant meteorological information (SIGMETs),  Airmen’s Meteorological Information (AIRMETs), and other  products are now readily accessible at any time during flight.  Weather products provided by cockpit weather systems are  typically presented on an MFD. Some installations allow  the overlay of this data in the PFD. You must learn the  procedures required to show each kind of weather product  on the MFD and/or PFD, and how to interpret each type  of weather product. Know the limitations of each type of  product, and the ways in which cockpit weather systems can  be used to gather information and remain clear of weather  hazards throughout the flight. A display that plainly shows your position with respect to  surrounding terrain is sometimes cited as the most reassuring  system available in the advanced avionics cockpit. The  same display can also invite the unwary pilot to attempt  risky maneuvers. Suppose that, on a VFR flight to an airport  located in hilly terrain, you encounter a layer of fog at  1,100 feet. In an aircraft with no terrain system, you would  not consider proceeding to the airport because you have a  personal minimum of 1,500 feet. With a ceiling of less than  1,500 feet, you deem the situation simply too risky. With the  surrounding terrain neatly displayed in front of you, however,  you may feel more confident and be tempted to give it a try.  However, a wise pilot remembers that, unless the equipment  is TAWS certified, accuracy is suspect. Even with TAWS  certification, the information presented is no better than  the database accuracy. Consult the equipment handbook or  manual to determine the accuracy of the database in that area. CFIT accidents are still occurring despite the advent of  advanced avionics. What has happened here? Psychologist  Gerald J. S. Wilde coined the phrase risk homeostasis to refer  to a tendency for humans to seek target levels of risk. Our  hill-flying scenario illustrates the concept. After pondering  the perceived risks, you decide that having the terrain display  gives you the same level of perceived risk with a 1,000‑foot  ceiling as you felt you had at 1,500 feet without the terrain  display. You see no need to “give away” this new margin  of perceived safety. Rather, you decide to use it to your  advantage. Equipped with the terrain display, your new  minimum ceiling becomes 1,000 feet, and you continue on  your way to the airport. Thunderstorms and general areas of precipitation are  detected through the use of radar. In the advanced avionics  cockpit, radar data can come from one of two sources:  an onboard weather radar system or a ground weather  surveillance radar system, such as the Next Generation  Radar (NEXRAD) system. Ground weather surveillance  system data is transmitted to the cockpit via a broadcast (or  datalink) weather service. Onboard weather radar and ground  weather surveillance radar systems each offer advantages and  disadvantages to the pilot. Some aircraft use a combination  of both systems. While onboard radar is real time, many downloaded radar  images and other reports are delayed for some time period  for various reasons. Given the nature of thunderstorms and  other weather hazards, this delay could prove hazardous. You  must know the true quality and age of the data. Most MFDs are capable of presenting radar data together  with aircraft position and the programmed route, as shown  in  Figure 5-11. Wilde does not support the idea of using technology to seek  target levels of risk. Rather, he argues that safety measures  such as seat belt laws and anti‑lock brakes have not resulted  in drastic reductions in highway fatalities in part because,  in response to the added sense of safety provided by these  measures, drivers have emboldened their driving behavior  to maintain existing levels of risk. Another issue is the lack of training in the new equipment  and its uses. The functions of TAWS and basically how  it works have been previously described, yet there is no  training program outside the military that teaches anyone to  5-9