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Does an IFR Rating Make You a Safer Pilot?
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Causes of Fatal Accidents in Cessna 172/182 Aircraft
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By Douglas Boyd Ph.D. and Sally Sims
Introduction
While the thrill of flying is the driving force for most of our aviation pursuits, nevertheless, as pilots we cannot escape the fact that there are inherent dangers associated with the endeavor. Therefore, identifying accident causes in general aviation might be instructive for pilots, allowing them to avoid the various traps. Thus, we undertook a study to determine the various causes of fatal general aviation accidents for Cessna 172 and 182 aircraft involving pilots with a private pilot rating (VFR) with, or without, an additional instrument rating (IFR).
Methods
We searched the NTSB web site (www.ntsb.gov/ntsb/query.asp) for fatal accidents of Cessna 172/182s for the period 1994 to1999. These aircraft were selected on the grounds that both are used by VFR-rated and IFR-rated pilots. A fatal accident was defined as one resulting in the death of a crew member. Weather conditions, pilot rating, hours logged and accident causes were retrieved. Student pilots were excluded from the study. Information missing from the NTSB web site was kindly provided by this agency (courtesy of Melba Moyer). A database (FileMaker Pro) was implemented using the above criteria and NTSB data.
Results
For the period 1994-1999, a total of 125 complete records were retrieved, and we were pleasantly surprised by the relatively small number of fatal accidents. Of these accidents, 67 were attributed to VFR-rated pilots, with the remaining 58 being ascribed to IFR-rated pilots. Accident causes were divided into those occurring under visual meteorological conditions (VMC) and instrument meteorological conditions (IMC).
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Accident Causes in Visual Meteorological Conditions (VMC)
There were 41 fatal accidents for VFR-rated pilots in Cessna 172/182s, compared with 35 for IFR-rated pilots. Of these accidents, NTSB determined probable causes for all but 5 of the accidents (involving 4 VFR-rated; 1 IFR-rated pilots). The main cause of fatal accidents for the VFR-rated pilots fell into the category of Stall/Spin/Loss of Control (15 accidents or 42%) (Figure 1). In contrast, IFR-rated pilots fared much better with only 21% (7) of the accidents falling in this category. It may be that this reduced accident rate for the IFR-rated pilots reflects the additional training and the emphasis placed on coordinated turns.
The second largest cause of fatal accidents in VMC was the controlled flight into either an obstacle or the ground, referred to by the NTSB as “Failure to Clear Terrain/Obstruction.” For VFR-rated pilots, slightly more (36%, 13 accidents) and for IFR-rated pilots, slightly less (29%, 10 accidents) than one third of the fatal accidents were attributed to this cause. The reasons for “running into obstacles” were varied and included, among others, unmarked power lines, pilot distractions, and intentional low flight. For VFR-rated and IFR-rated pilots 5/13 and 2/10 of the accidents in this category occurred at night respectively. The higher rate of accidents at night for the former group might explain why some fixed base operators/insurance companies have banned night flight for VFR-rated aviators.
One striking feature in the analysis of accidents in VMC was the high number of midair collisions for the IFR-rated pilots (6 or 18% of the accidents). In contrast, of the 41 fatal accidents for VFR-rated pilots, only 1 (3%) was attributed to this cause. It may be that with the emphasis on “instrument scanning” in the training of IFR-pilots, this group has a difficulty in shifting into “VFR-mode,” where the responsibility for traffic separation lies with the pilot. (FAA regulations specify that 70% of the time should be spent looking for traffic). It is worth noting that all of these midair collisions occurred while flying under visual flight rules.
Improper procedures/Planning was a less frequent cause of fatal accidents for both VFR- and IFR-rated pilots (<15% for both groups) and occurred at similar rates for both groups. These included a multitude of improper procedures including incorrect weight/balances, disregard for increased density altitude, fuel exhaustion, carburetor icing, and improper use of flaps.
On a more positive note, it was encouraging to discover that engine failure (Malfunction category) was an infrequent cause of fatal accidents. There were only 5 fatal accidents (3 IFR-rated and 2 VFR-rated pilots) total for both groups of pilots in these aircraft. Review of the NTSB reports indicated that of the 5 accidents, only one was deemed in an area unsuitable for landing. Had the pilots maintained aircraft control in the other 4 cases, it is very possible that fatalities could have been avoided.
In addition to the above mentioned accident causes, rare instances occurred where the NTSB cited other causes. Due to their infrequency, we grouped them together under “Other” category and these accounted for <10% of the accidents for either group. Accident causes included contaminated fuel, turbulence, and pilot intoxication. Of these accidents, 3 were incurred by IFR-rated pilots and 1 by a VFR-rated aviator.
Accident Causes in Instrument Meteorological Conditions (IMC)
Of the accidents in IMC, 26 and 23 were attributed to VFR- and IFR-rated pilots respectively. It should be emphasized that the similar fatality rate of VFR- and IFR-rated pilots does not suggest that the former group are in any way equipped for these conditions. Rather, the data simply reflect a larger number of IFR-rated pilots who fly in IMC in contrast to VFR-rated pilots who, in the main part, steer clear of such conditions.
Expectedly, the biggest killer (62% of accidents) for VFR-rated pilots was Stall/Spin/Loss of Control as a direct consequence of spatial disorientation (Figure 2). In contrast, IFR-rated pilots, with their instrument skills, suffered a much lower accident rate in this category (26% of the fatal accidents). These finding are not at all surprising since it is well established that VFR-rated pilots just do not have the instrument training to tackle IMC.
Decreasing cloud bases often lead to both VFR- and IFR-rated pilots scurrying under the cloud layer in an attempt to avoid the IMC. Unfortunately, and too often, low altitude flying has the undesired consequence of an “encounter” either with an obstruction or the ground. This “failure to clear terrain/obstruction” category accounted for 39% of accidents for both VFR-rated and IFR-rated pilots. Certainly, VFR-rated pilots have little alternative in the event of encountering unexpected IMC. However, their IFR-rated counterparts might have avoided these accidents by requesting a “pop-up” IFR clearance upon confronting such weather.
Three other categories of accidents under IMC were solely the domain of the IFR-rated pilots. First, improper procedures/planning (failure to maintain the ILS glideslope, and incorrect weights and balances) accounted for 5 (22%) of the accidents by IFR-rated pilots. There was one instance of an inoperable artificial horizon (Malfunction category), and two accidents in the “Other” category, one involving icing and the other attributed to pilot intoxication. With the exception of the accidents related to pilot intoxication and weight/balance, these findings are not surprising, considering the demands put on the pilot by IMC. As an aside, it is heartening to note that of the 49 accidents in IMC, only one was attributed to equipment failure.
Benefits of an IFR-rating
A statement often heard from flight instructors is that the instrument rating “will make you a better pilot.” Certainly, our data indicates that this rating has some clear benefits both under VMC and IMC conditions. Notably, IFR-rated pilots enjoy a 50% reduction in the Stall/Spin/Loss of Control category under both VMC and IMC conditions when compared with their VFR-rated counterparts. On the other hand, the IFR-rated group got snared by other causes that seem to impact the VFR-rated cohort less often. First and foremost, the 6-fold higher mid-air collision rate under VMC conditions by the former group was obvious. Second, under IMC, following improper procedures leads to deadly consequences for IFR-rated pilots, this presumably reflecting the unforgiving environment.
In total (both VMC and IMC accidents), there were 67 and 58 fatal accidents involving VFR-rated and IFR-rated pilots respectively. However, in general aviation, VFR-rated pilots (258,749) outnumber their IFR-rated peers (171,309) (source: AOPA, www.aopa.org/whatsnew/stats/). Correcting for this increased presence of VFR-rated pilots, we calculated 26 fatal accidents per 100,000 VFR-rated and 34 fatal accidents per 100,000 IFR-rated pilots. The slightly higher rate for the IFR-trained pilots did not represent skewing of the data under the more strenuous demands of IMC, since a similar trend was evident under VMC conditions (16 and 21 fatal accidents per 100,000 VFR- and IFR-rated pilots respectively). Likewise, increased exposure of IFR-rated pilots, who generally have higher flight times than their VFR-rated counterparts, is unlikely to be the cause of the increased accident rate for the former group. Thus, for pilots with 200-1000 logged hours, the fatality rate was 9 VFR-rated pilots and 10 IFR-rated pilots per 100,000 pilots with the corresponding rating. Taken together, our findings, albeit with these aircraft, would suggest that while IFR-rated pilots do indeed have a greater control of the aircraft, this rating does not confer a lower fatal accident rate.
Summary
The loss of aircraft control for VFR-rated pilots under VMC is the largest cause of fatal accidents, a rate that is halved for their IFR-rated counterparts. Second to this cause, both groups of pilots suffer from high rates of ground/obstacle “encounters” under clear skies while IFR-rated pilots experienced a substantially higher rate of midair collision.
In IMC, loss of aircraft control and “scud running” accounted for all of the VFR-rated pilot accidents. In contrast, their IFR-rated counterparts, showed superior flight control, as evidenced by a 50% reduction in this accident category. Unfortunately, this safety margin for the IFR-rated group was offset by accident causes related to improper procedures as well as rare events such as equipment failure, icing, and pilot intoxication.
Overall, IFR-rated aviators showed a slightly higher fatal accident rate compared with the VFR-rated cohort. The increased accident rate was not due to the more demanding IMC environment, since a similar trend was evident under VMC.
Dr. Douglas Boyd (doug1961@aol.com) holds a Private Pilot with Instrument rating. Sally Sims (sallysue@onramp.net) holds Private Pilot, Instrument, Multiengine, and CFI ratings and is an Aviation Safety Counselor.
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