Related Experiment Video
Updated: Jul 10, 2026
08:36
Collecting Sleep, Circadian, Fatigue, and Performance Data in Complex Operational Environments
Published on: August 8, 2019
Aircraft crash rates and cumulative hours: USAF data for 25 airframes, 1950-2006
Terence J Lyons1, William Nace
1Air Force Office of Scientific Research, 875 N. Randolph St., Ste. 325, Rm. 3112, Arlington, VA 22203-1768, USA. terence.lyons@afosr.af.mil
Aviation, Space, and Environmental Medicine
|October 25, 2007
Summary
Aircraft crash rates decrease with increased flight hours, demonstrating significant organizational learning in both manned and unmanned systems. This inverse relationship indicates continuous improvement in aviation safety over time.
Area of Science:
- Aerospace Engineering
- Aviation Safety
- Human Factors in Aviation
Background:
- Aircraft crash rates are a critical concern for aerospace safety researchers, the aviation industry, and the public.
- Understanding long-term trends in aviation accidents is essential for improving safety protocols.
Purpose of the Study:
- To analyze the relationship between cumulative flight hours and crash rates in U.S. Air Force aircraft.
- To determine if aircraft age correlates with an increased risk of crashes.
Main Methods:
- Utilized U.S. Air Force Safety Center data for major accidents (Class A Mishaps) and flight hours from 1950-2006.
- Applied regression analysis to the logarithmic transformation of cumulative flight hours and crash rates for individual aircraft models.
Main Results:
- A significant inverse power-law relationship (y = bt^m) was observed between crash rate and flight hours for most aircraft (r² = 0.78-0.99).
- Negative exponents (-0.25 to -0.75) indicate decreasing crash rates with increased flight hours across fighter, attack, training, bomber, and transport aircraft.
- The Predator unmanned aircraft also exhibited this learning trend, with a slope of -0.37.
Conclusions:
- A strong inverse correlation between flight hours and crash rates signifies substantial organizational learning and safety improvements in most USAF aircraft.
- Learning and safety improvements extend to unmanned aircraft systems, mirroring trends in manned aviation.
- The study found no evidence to support an increased crash risk associated with aircraft aging.
Related Concept Videos
01:21Fatigue
Fatigue occurs when materials rupture under repeated or fluctuating loads, even at stress levels far below their static breaking strength. It typically results in brittle failure, even for ductile materials. It is a critical consideration in designing machines and structural components subjected to repetitive or varying loads. The nature of these loadings can range from fluctuating loads like unbalanced pump impellers causing vibrations to repeatedly bending a thin steel rod wire back and forth...
01:16Hypothesis Test for Test of Independence
The test of independence is a chi-square-based test used to determine whether two variables or factors are independent or dependent. This hypothesis test is used to examine the independence of the variables. One can construct two qualitative survey questions or experiments based on the variables in a contingency table. The goal is to see if the two variables are unrelated (independent) or related (dependent). The null and alternative hypotheses for this test are:
H0: The two variables (factors)...
H0: The two variables (factors)...
01:11Hazard Rate
The hazard rate, also known as the hazard function or failure rate, is a statistical measure used to describe the instantaneous rate at which an event occurs, given that the event has not yet happened. From a probabilistic perspective, it represents the likelihood that a subject will experience the event in a very small time interval, conditional on surviving up to the beginning of that interval. In terms of frequency, the hazard rate can be viewed as the ratio of the number of events to the...
01:13Impulse
According to Newton’s second law of motion, the rate of change of the momentum of an object is the net external force acting on it. The total change in momentum between two timepoints thus depends on both the external force acting on it and the time over which it acts. Describing this mathematically, the total change of an object’s motion is proportional to the force vector and the time over which it is applied. This product is called impulse.
Additionally, it can be shown that the total...
Additionally, it can be shown that the total...
01:08Determination of Expected Frequency
Suppose one wants to test independence between the two variables of a contingency table. The values in the table constitute the observed frequencies of the dataset. But how does one determine the expected frequency of the dataset? One of the important assumptions is that the two variables are independent, which means the variables do not influence each other. For independent variables, the statistical probability of any event involving both variables is calculated by multiplying the individual...
01:21Types of Reports II: Incident or Occurrence Report
An Incident or Occurrence Report in a healthcare setting is a crucial document used to record any unexpected occurrence that may or may not have affected a patient, employee, or visitor. Such reports are critical to improving patient safety and include all details leading up to and including the event.
Purposes:
In the healthcare industry, reports play a crucial role in documenting incidents within an agency. The primary objective of these reports is to ensure patient safety, uphold the...
Purposes:
In the healthcare industry, reports play a crucial role in documenting incidents within an agency. The primary objective of these reports is to ensure patient safety, uphold the...