terrain avoidance

June 11, 2020

Controlled flight into terrain accidents afflict pilots of all skill levels. Capt. Leroy Cook advises to always maintain situational awareness to avoid such occurrences

Controlled Flight Into Terrain (CFIT) is not a phrase and acronym any pilot wants to have associated with a report concerning his or her flight – not that they are likely to be around to read it. The term is a convenient, simplistic way of assigning an obvious cause to an aircraft accident, and yet it means very little in and of itself.

Quite clearly, CFIT results from a loss of situational awareness; no one of sound mind intentionally steers an airplane into a mountain or lets his altitude dwindle until it reaches zero. Had the crew been keeping track of the flight situation, the crash wouldn’t have happened. Typically, CFIT accidents don’t occur in a Loss Of Control In Flight (LOC-I) circumstance; rather, they would seem to be the result of sheer carelessness. The aircraft impacted the ground while fully capable of being flown away from danger, but it wasn’t.

And so, CFIT does happen, all the best intentions by the crew notwithstanding. There were 28 such accidents recorded during the years 2013 to 2017. And since there is an 89% fatality rate associated with CFIT mishaps that makes them especially significant, even while being relatively small in number.

Terrain Awareness Warning System (TAWS) mandates, formerly called Enhanced Ground Proximity Warning Systems (EGPWS), are supposed to have eliminated CFIT accidents, but the creativity of the human mind, with its innate ability to thwart technology, cannot be entirely legislated away. Certainly, our friendly “Rock Monitors” have served us well with their “terrain, terrain” and “pull up, pull up” warnings, but there are still intervening circumstances that cause the pilot flying to ignore those stern voices.

How can we make sure we’re never the subject of a CFIT finding? Simply by remaining situationally aware. That can be easier said than done; our fine moving maps, for the most part, are two-dimensional in their depiction. CFIT involves the third dimension, so we need to not only keep away from the approaching terrain laterally, we also must monitor our true altitude, the all-important height above the ground.

How can we mess up that simple task? Over-reliance on technology is one of the chief contributors. We tend to set the altitude pre-select on a target and expect the aircraft to level off accordingly—but if we give the autopilot an incorrect number, or fail to assure it was armed, it will dutifully fly us into the ground. Or, we may accept radar vectors to the initial approach fix and fly the assigned heading without question, expecting the controller to turn us before impact. In both cases, pilot-induced or ATC-induced, the catastrophic outcome can only be prevented by maintaining situational awareness.

The CFIT danger remains ever with us, even in this day and age marked by an overabundance of information, displayed in graphic form right on our glass panels. We can see the depicted terrain turn red, we can hear chimes and alerts, but if we’re not focused on the job immediately before us, all may be lost. Distraction from that vital task of avoiding terrain is a major contributor to pilot-induced CFIT accidents.

If our attention is diverted by flight-related tasks, such as a system fault that needs troubleshooting or an unexpected change in arrival runway, we can quickly lose situational awareness, and not recover it before it’s too late. Or, we may “tune out” the TAWS and synthetic vision alarms because the last stages of the approach into a tricky airport involves some creative nap-of-the-earth flying that requires ignoring the terrain warnings. In the first case, we didn’t know we were flying toward rising terrain. In the latter, we knew it, but thought we still had room to maneuver.

Business aircraft are particularly susceptible to CFIT risks, because they are often flown into out-of-the-way airports that are convenient for the passengers, destinations that are unfamiliar to the pilots and not always equipped with airline-style approach aids. Corporate helicopter operations are at greatest risk, frequently flying at low altitude under visual flight rules, many times flown by a single pilot.

Pay Attention

To protect ourselves from becoming a CFIT statistic, we must straighten up and heighten our awareness during the takeoff and landing stages of the flight, when most of these accidents happen. Take care to emphasize the “sterile cockpit” rule below 10,000 feet AGL; relieving boredom with intra-cockpit banter is fine during the cruise phase of flight, but not when flying down among the rocks. CRM needs to be employed effectively during arrival and departure segments; both the PF and PNF must verify crossing altitudes, check data inputs and generally keep track of where the aircraft is, in relation to where it should be next.

Altimetry errors cannot be discounted as a cause of CFIT accidents. We were all taught the training mantra “cold or low, look out below,” meaning that an uncorrected altimeter setting when flying into cold air or lower pressure conditions will result in the aircraft being lower than the altimeter indicates. Approaches at airports combining intervening high terrain and extreme cold weather may require raising the published altitudes to ensure a safe margin. Some altimeter setting scales may not even have the capacity to adjust for the high pressure inherent in super-cold conditions.

Don’t Miss the Step

The time-honored design method for non-precision IAP’s with terrain issues is to impose “step-down” fixes at intervals on the way from the FAF to the MAP. Pilots are to stop their descent if they reach the published crossing altitude before passing the fix, resuming descent after passing the waypoint. Such interrupted descents are a set-up for CTAF accidents, as pilots have to remember not just the IAP’s minimum descent altitude, but one or more extra descent limits. Distracting workload results from the multiple power and attitude changes required. A better solution is to use a tabulated constant-angle descent, as opposed to the “dive and drive” taught in basic instrument flying. Constant-angle non-precision approaches use DME distance and altitude inputs to keep the aircraft on a three-degree slope to the MAP, freeing the pilot-flying from repeatedly leveling off and re-establishing descent.

CFIT Accidents That Should Not Have Happened

A tragic ending to Korean Air Flight 801’s journey from Seoul to Guam on 5 August 1997 occurred because of several neglected issues. There was restricted visibility on a rainy night, an inoperative ILS and a lack of cross-checking by the Boeing 747’s three cockpit crew members; all of these factors inhibited situational awareness. The aircraft hit a 660-foot hill three miles short of the runway, even though GPWS had sounded a pull-up warning. Three contributing factors were too many.

Another 747 crashed at Kuala Lumpur, Malaysia on 19 February 1989 during an NDB approach when the crew followed incorrectly-stated ATC instructions of “descend two four hundred”; the published segment of the approach was 2400 feet. Instead, the Flying Tigers Airline crew descended to 400 feet, as they thought they were instructed; eight GPWS warnings later, the aircraft flew into a low mountain. Clearly, there was an ATC error, but the pilots should have kept up their situational awareness and abandoned the approach at the first ground-proximity warning.

An HS-125 business jet departed San Diego, California USA late at night on 8 March 1981 and was only in the air for four minutes before hitting a 3472-foot mountain. The crew had elected to depart under VFR and pick up their IFR clearance in flight, but failed to climb out of concern for overhanging Class B airspace (even though Class B did not begin until 5800 feet). Again, situational awareness was not maintained, perhaps due to schedule pressure, airspace distractions and darkness.

The most recent CFIT of note took place on 26 January 2020, when a Sikorsky S-76B helicopter impacted a fog-shrouded hilltop north of Los Angeles, California USA. As is typical for rotary-wing operation beneath congested airspace, the flight was conducted under VFR, by following major highways. But marine fog obscured the route in the hills that were encountered during the final stages of the otherwise-routine trip, and the pilot indicated to ATC that he was climbing from 1500 feet to 4000 feet to avoid a cloud layer that had dropped to ground level. Unfortunately, spatial disorientation caused a LOC-I during the short climb and the helicopter descended rapidly into the unseen rising terrain at 1085 feet MSL. Here, positional awareness was being rigorously maintained but the transition from marginal VMC to full IMC overcame the single pilot, even though he was IFR rated. Overconfidence and pressure to meet a customer’s expectations contributed to the deaths of nine persons.

These and other CFIT accidents point out the need to always maintain situational awareness. That seems simple and obvious, until intervening factors, such as distractions, shortcutting of procedures, disagreeing instrument indications, and over-reliance on automation, take over the pilot’s focus. Watch for such preoccupying issues that cause you miss an altitude target or fail to communicate with other crew members. And don’t forget to look out the windows occasionally!