Tools for Hazard Awareness
There are some basic tools for helping recognize hazards.
Advisory Circulars (AC)
Advisory circulars (ACs) provide nonregulatory information for helping comply with 14 CFR. They amplify the intent of the regulation. For instance, AC 90-48, Pilot’s Role in Collision Avoidance, provides information about the amount of time it takes to see, react, and avoid an oncoming aircraft.
For instance, if two aircraft are flying toward each other at 120 knots, that is a combined speed of 240 knots. The distance that the two aircraft are closing at each other is about 400 feet per second (403.2 fps). If the aircraft are one mile apart, it only takes 13 seconds (5,280 ÷ 400) for them to impact. According to AC 90-48, it takes a total of 12.5 seconds for the aircraft to react to a pilot’s input after the pilot sees the other aircraft. [Figure 1-1]
Figure 1-1. Head-on approach impact time.
Understanding the Dangers of Converging Aircraft
If a pilot sees an aircraft approaching at an angle and the aircraft’s relationship to the pilot does not change, the aircraft will eventually impact. If an aircraft is spotted at 45° off the nose and that relationship remains constant, it will remain constant right up to the time of impact (45°). Therefore, if a pilot sees an aircraft on a converging course and the aircraft remains in the same position, change course, speed, altitude or all of these to avoid a midair collision.
Understanding Rate of Climb
In 2006, a 14 CFR part 135 operator for the United States military flying Casa 212s had an accident that would have been avoided with a basic understanding of rate of climb. The aircraft (flying in Afghanistan) was attempting to climb over the top ridge of a box canyon. The aircraft was climbing at 1,000 feet per minute (fpm) and about 1 mile from the canyon end. Unfortunately, the elevation change was also about 1,000 feet, making a safe ascent impossible. The aircraft hit the canyon wall about ½ way up the wall. How is this determined? The aircraft speed in knots multiplied by 1.68 equals the aircraft speed in feet per second (fps). For instance, in this case if the aircraft were traveling at about 150 knots, the speed per second is about 250 fps (150 x 1.68). If the aircraft is a nautical mile (NM) (6,076.1 feet) from the canyon end, divide the one NM by the aircraft speed. In this case, 6,000 feet divided by 250 is about 24 seconds. [Figure 1-2]
Figure 1-2. The figure above is a scale drawing of an aircraft climbing at 1,000 fpm, located 1 NM from the end of the canyon and starting from the canyon floor 1,000 feet below the rim. The time to cover 6,000 feet is 24 seconds. With the aircraft climbing at 1,000 fps, in approximately ½ minute, the aircraft will climb only 500 feet and will not clear the rim. [click image to enlarge]Understanding the Glide Distance
In another accident, the instructor of a Piper Apache feathered the left engine while the rated student pilot was executing an approach for landing in VFR conditions. Unfortunately, the student then feathered the right engine. Faced with a small tree line (containing scrub and small trees less than 10 feet in height) to his front, the instructor attempted to turn toward the runway. As most pilots know, executing a turn results in either decreased speed or increased descent rate, or requires more power to prevent the former. Starting from about 400 feet without power is not a viable position, and the sink rate on the aircraft is easily between 15 and 20 fps vertically. Once the instructor initiated the turn toward the runway, the sink rate was increased by the execution of the turn. [Figure 1-3] Adding to the complexity of the situation, the instructor attempted to unfeather the engines, which increased the drag, in turn increasing the rate of descent as the propellers started to turn. The aircraft stalled, leading to an uncontrolled impact. Had the instructor continued straight ahead, the aircraft would have at least been under control at the time of the impact.
Figure 1-3. In attempting to turn toward the runway, the instructor pilot landed short in an uncontrolled manner, destroying the aircraft and injuring both pilots.
There are several advantages to landing under control:
- The pilot can continue flying to miss the trees and land right side up to enhance escape from the aircraft after landing.
- If the aircraft lands right side up instead of nose down, or even upside down, there is more structure to absorb the impact stresses below the cockpit than there is above the cockpit in most aircraft.
- Less impact stress on the occupants means fewer injuries and a better chance of escape before fires begin.
Risk
Defining Risk
Risk is the future impact of a hazard that is not controlled or eliminated. It can be viewed as future uncertainty created by the hazard. If it involves skill sets, the same situation may yield different risk.
- If the nick is not properly evaluated, the potential for propeller failure is unknown.
- If the aircraft is not properly bonded and grounded, there is a build-up of static electricity that can and will seek the path of least resistance to ground. If the static discharge ignites the fuel vapor, an explosion may be imminent.
- A fatigued pilot is not able to perform at a level commensurate with the mission requirements.
- The owner of a homebuilt aircraft decides to use bolts from a local hardware store that cost less than the recommended hardware, but look the same and appear to be a perfect match, to attach and secure the aircraft wings. The potential for the wings to detach during flight is unknown.
In scenario 3, what level of risk does the fatigued pilot present? Is the risk equal in all scenarios and conditions? Probably not. For example, look at three different conditions in which the pilot could be flying:
- Day visual meteorological conditions (VMC) flying visual flight rules (VFR)
- Night VMC flying VFR
- Night instrument meteorological conditions (IMC) flying instrument flight rules (IFR)
In these weather conditions, not only the mental acuity of the pilot but also the environment he or she operates within affects the risk level. For the relatively new pilot versus a highly experienced pilot, flying in weather, night experience, and familiarity with the area are assessed differently to determine potential risk. For example, the experienced pilot who typically flies at night may appear to be a low risk, but other factors such as fatigue could alter the risk assessment.
In scenario 4, what level of risk does the pilot who used the bolts from the local hardware center pose? The bolts look and feel the same as the recommended hardware, so why spend the extra money? What risk has this homebuilder created? The bolts purchased at the hardware center were simple low-strength material bolts while the wing bolts specified by the manufacturer were close-tolerance bolts that were corrosion resistant. The bolts the homebuilder employed to attach the wings would probably fail under the stress of takeoff.
