High At Night

A nighttime Bonanza crash is blamed on spatial disorientation. But what about hypoxia or illusions?


These pages often have extolled the virtues of night flying, with less traffic and smoother air foremost among them. In almost the same breath, however, we also caution against the many ways night flying can trip us up. Yes, our basic inability to, you know, actually see things outside the airplane can be a problem, but that’s only part of the challenges we face when flying at night.

One of the principal considerations of night flying is the human eye’s limitations, especially those involving depth and color perception. These considerations can be addressed—but not eliminated—by using supplemental oxygen. Other, more mundane night-flying concerns include so-called “black hole” approaches as well as the inability to observe and remain clear of obstacles when landing or taking off. All these failings of the human eye and the ways in which we operationally compensate for them can be complicated when we’re oxygen deprived.

Another problem with oxygen deprivation is our simple inability to reason effectively, make decisions and implement them. In fact, this lethargy is one of the many telltale signs I use to know when I need to use supplemental oxygen regardless of the time of day.

After an hour or so at or above 10,000 feet, strapping on a cannula and cranking open the O2 bottle often has an immediate effect. At night, the effect is even greater, and resembles flying from an area with restricted visibility into one with CAVU weather. That’s one reason the U.S. Department of Defense’s joint Oxygen Systems Handbook states, “Oxygen is recommended on all aircraft with night flights operating above 5000 feet to enhance night vision capability.” Age, tobacco use and overall physical condition are just as important as altitude when determining minimum altitudes at which to use supplemental oxygen. Here’s an example of what can happen when we ignore good advice like this.

On January 6, 2011, at about 1845 Pacific time, a Beech S35 Bonanza impacted the frozen shoreline of a lake adjacent to Rogers Field Airport (O05) in Chester, Calif. The private pilot and passenger were killed. The airplane sustained substantial damage to both wings and the entire fuselage forward of the tailcone. Visual night conditions prevailed.

A witness, who was a neighbor of the pilot, heard the pilot report over the radio that he was overflying the airport for a right base traffic pattern entry. The witness could hear but not see the airplane. A second witness also heard the airplane and observed its lights fly from left to right in a gradual descent. The lights descended behind trees, and toward the lake. She then heard the sound of a thud, followed by the noise of cracking ice.

Radar data for the flight depict it flying above 10,000 feet msl for about 31 minutes. The data show the airplane climbing as high as 11,100 feet, with the final radar return occurring at 11,000 feet and about 18 miles southwest of the accident location. The airport’s field elevation is 4534 feet msl; its traffic pattern altitude is 5534 feet.

The accident site elevation was 4500 feet msl, about 3500 feet northeast of the approach end of Runway 34. The debris field was about 900 feet long, on a bearing of 160 degrees, parallel to the runway. The first identified point of impact was characterized by a 12-inch-deep, 7-foot-long, teardrop-shaped swath of excavated snow. The ground excavation was oriented on a bearing of about 150 degrees. A second swath was located about 15 feet beyond the initial impact.

All major portions of the airplane were accounted for at the accident site, and no indications of pre- or post-impact fire were observed. The airplane’s wing flap and landing gear mechanisms indicated both these systems were in the fully retracted position at impact. The aftermarket speed brake system displayed witness marks consistent with being retracted prior to impact, with subsequent extension and paddle over-travel caused by cable pull-through during impact. The propeller blades exhibited signs of rotating under power at impact, and the vacuum pump could be rotated by hand in a smooth and unrestricted movement. No evidence of catastrophic malfunction was noted.

The left wing’s fuel tank contained approximately 25 gallons of a fluid consistent in color and odor to aviation gasoline. There were no anomalies with the airframe or engine precluding normal operation. The airplane was not equipped with a supplemental oxygen system.

The 76-year-old pilot held a private pilot certificate and did not have an instrument rating. His two most recent applications for a third-class Airman Medical Certificate, dated 5/1/2007 and 4/21/2009, indicated “No” in response to “Do You Currently Use Any Medication,” and to all items under “Medical History,” including specifically “Heart or vascular trouble,” “Diabetes,” “Admission to hospital,” and “Other illness, disability, or surgery.” Personal medical records, however, noted a “mild heart attack” in October 2005, treatment for high cholesterol since that time and a diagnosis of diabetes in November 2005. Autopsy results noted arterial stents were present.

Weather at an automated station about 10 miles east of the accident site at 4994 feet included calm winds, a temperature of two degrees C a dew point of minus six degrees C, and an altimeter setting at 30.25 inches Hg. The NTSB noted, “The pilot’s forward view would also have been dominated by a dark void as the airplane passed over the town, and began the landing approach.”

Probable Cause
The NTSB determined the probable cause(s) of this accident to include: “The pilot’s loss of control while maneuvering to land, most likely due to spatial disorientation.” Except that it’s not at all clear from the accident record that the pilot lost control. In fact, it seems he flew the airplane into the ground while maneuvering in the traffic pattern. The question is why.

An obvious answer is the pilot lost situational awareness about how high he was in relation to the runway. Since he frequently used the airport he was approaching, it’s unlikely he was confused about the airplane’s position. But after spending some 30 minutes at or above 10,000 feet, followed by a quick descent to a traffic pattern altitude above 5000 feet msl, the idea this 76-year-old pilot’s night vision was impaired isn’t far-fetched. Remember that the next time you’re on a night cross-country.




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