Recovering 1s and 0s
By Bill Tuccio, PhD, ATP, CFII/MEI
This is the third blog in a new series of posts about the NTSB’s general aviation investigative process. This series, written by NTSB staff, explores how medical, mechanical, and general safety issues are examined in our investigations.
I joined the NTSB in 2010 as a recorder investigator in the Vehicle Recorders Division. I work to recover “1s and 0s” from electronics, including cockpit voice and flight data recorders (aka “black boxes”) and video sources. As a recorder investigator, I work early in the investigative lifecycle to create factual reports of electronic data: if it might record something and has a green board or a little chip, we’re interested.
My formal training and experience is in aeronautical engineering, aviation, computer/database/iOs programming, and conversation analysis. I’m also a flight instructor, former regional airline captain, and aircraft owner. Through my work on more than 400 NTSB investigations and my 30 years as a flight instructor, I’ve had some incredible moments, but my most memorable is soloing my son in our tailwheel Maule on his 16th birthday. We enjoyed the usual fun so many pilots experience on soft fields, and it was a success. Now, about 10 years later, my son is a certified flight instructor-instrument (CFII) who has taught his own students.
Soft fields are fun, but they also carry risks that pilots have to manage. The FAA Airman Certification Standards (ACS) for private and commercial pilots include soft-field takeoffs and the separate (but arguably related) short-field takeoffs.
What do soft and short fields have to do with readouts of recorded data? Normally, nothing. When something goes wrong, however, the data can sometimes help piece together the story.
I recovered data from electronic devices in two soft-field investigations. Unfortunately, there were no survivors in either accident, but these fatal crashes highlight some of the risks noted in the ACS.
The first case involved a 1956 Cessna 172 in Veneta, Oregon, with four people on board. The airplane was just below gross weight and within center-of-gravity limits. According to other investigative information, the grass of the 3,200-foot runway was mowed to about 3 inches in height and was damp from a prior rain shower.
I was given an iPhone recovered from the passenger in the right front seat. It yielded some photos of the pilot and passengers before boarding and a video of the first 23 seconds of the accident flight. Below is a picture taken before boarding, showing the accident airplane with the runway environment behind. The tall grass immediately apparent in the photo obscures the runway, which is further in the background. This photo was useful to corroborate the weather conditions at the time of the accident.
The 23-second video also helped. It began when the aircraft was on its takeoff roll. We worked with the raw video as recorded, rather than subject it to labor-intensive postprocessing, which is sometimes necessary to stabilize the constantly shifting camera angle of an iPhone video. One significant feature of the video was that from the 15-second mark until the end of the recording, we could hear a sound similar to the stall warning. Some partial views of the instruments supported other evidence indicating that the engine was operating properly.
When combined with other investigative evidence, the NTSB determined the probable cause of this accident was “The pilot’s failure to maintain adequate airspeed and altitude to clear trees during takeoff initial climb.” (You can access the detailed factual reports here: https://go.usa.gov/xRGGe.) I often use this case while teaching students about soft- and short‑field takeoffs to emphasize the ACS risks of collision hazards, including aircraft, terrain, obstacles, and wires; low altitude maneuvering, stall, and spin; and runway surface conditions.
The second soft-field/short-field case that rested (in part) on my work with recorded data was the crash of a 1977 Cessna T210M in Challis, Idaho, also with four people on board, loaded to 3,551 pounds (maximum gross weight for this plane was 3,800 pounds) and within center-of-gravity limits.
According to other investigative information, the 5,500-feet mean sea level airport had a 2,500‑foot turf/dirt runway, with an estimated density altitude during the accident of 6,046 feet. Because of terrain features, pilots generally landed on runway 22 and departed on runway 4. The accident flight was departing on runway 4.
Two significant electronic devices were recovered from this accident: a JPI EDM-700 engine monitor and a Garmin GPSMAP 496 portable GPS device. Both have recording capabilities, but each sustained impact and postimpact fire damage requiring chip-level data recovery. The figures below show the JPI EDM-700 and Garmin 496 chips that were recovered.
Using tools in our lab, we removed the chips and cleaned them up. We then “imaged” the chips (that is, created a file of all the 1s and 0s on the chip) using a commercially available chip programming device. Our frequent experience with the JPI EDM-700 and Garmin 496 contributed to our efficient data extraction from the binary image to produce useful engineering data.
In this case, the JPI EDM-700 recorded the takeoff and supported other investigative information showing that the engine was functioning properly. As you can imagine, when working with recovered avionics, data can be confusing; in this case, the end of the recording had unchanging data. By comparing the accident takeoff data with a prior takeoff, combined with our prior knowledge of the EDM-700 recording logic, we were able to attribute the unchanging data to invalid data after the aircraft had crashed.
The Garmin 496 recorded the accident flight and 49 prior flights. Although the accident flight was undoubtedly helpful to the investigation, we also decided to compare the accident takeoff to nine prior takeoffs on the same runway, considering groundspeed and lateral path. The accident flight differed from all prior flights in that prior flights proceeded to the right of the accident flight’s trajectory near the departure end of runway 4.
Investigators worked with Cessna to calculate the takeoff performance. With no wind, to clear a 50-foot obstacle, the airplane would need 2,231 feet of runway. With a 5-knot tailwind, the airplane would need 2,677 feet. The actual distance from the start of the takeoff roll to the point at which the aircraft struck the first 50-foot tree was 2,625 feet.
Our report noted, “In the takeoff configuration, with the nose-high pitch, it is possible that the pilot’s windscreen view of the terrain would be limited.” We determined the probable cause was “The pilot’s attempt to depart in conditions that resulted in the airplane having insufficient performance capability, which resulted in a collision with a tree.” (You can access the detailed factual reports here: https://go.usa.gov/xRGGd.)
I often use this accident to teach my students the ACS short-field knowledge areas of the “effects of atmospheric conditions, including wind, on takeoff and climb performance,” as well as risk management regarding the “selection of runway based on pilot capability, aircraft performance and limitations, available distance, and wind.”
As Mike Hart wrote in AVweb, “If the calculated length of the field is less than the number calculated from the POH, don’t even think about turning your prop. An obvious accident is avoided.” He goes on to add, if the calculated distance is at all close, check your math and your assumptions. Pilot technique and aircraft condition are just two factors that can make a world of difference.
The electronic devices you use when you fly can increase your situational awareness and enjoyment. Some devices empower you to check historical engine trends and identify mechanical issues early. And, in the relatively rare cases when things go wrong, we can use this electronic information—all those 1s and 0s—to dig deeply into what went wrong and how, and help avoid a similar outcome in the future.