Purpose of Bowtie Analysis in Aviation SMS Programs

Bowtie analysis is one of the most thorough aviation risk management tool. It analyzes safety events from all essential risk management viewpoints, including root causes, hazards, risks, controls, and consequences.

If you are not using bowtie analysis, here are some of it's common uses:

  • Risk scenario analysis;
  • Demonstrating potential costs of a scenario to executive management;
  • Demonstrate the importance of compliance;
  • Teach what risk management is;
  • Safety incident management;
  • Risk control and root cause analysis; and
  • Safety event summary.

Creating quality bowties takes practice. Here are the 6 steps to perform bowtie analysis in aviation SMS.

Bowtie analysis in aviation SMS 5 step walkthrough

One: Establish Top Event

Step one is the most critical step. You need to choose the Top Event. The Top Event is:

  • The risk event (similar to hazard, depending on how you define hazard);
  • The point at which safety control is/was lost; and
  • The point that root causes lead to, and that eventually results in damages.

It's extremely important to find a good point at which safety control is lost, as the rest of the bowtie will depend on it.

Two: Establish Preceding Events and Root Cause Threats

Now what needs to be done is to work backwards, listing each event step by step that lead to the Top Event. As each event is listed, ask “But why did this happen?” Eventually we are looking for the root cause threats. This is a similar process to the 5-Whys root cause analysis. A good indication that you have arrived at root causes is when your answer to the question is, “Just because.”

The purpose of this activity is to document the link between root causes and the Top Event. This will help clarify:

  • Which risk controls failed;
  • How Human Factors and behavior played a role in the elevation of danger; and
  • What the root causes.

Notice that distraction and Human Error are perfectly valid root causes, as sometimes we simply are distracted or make mistakes for no “good reason.” For some reason, some organizations seem to feel that Human Error is not a valid root cause. This is an erroneous belief and will hinder root cause analysis.


Aviation Bowtie analysis step 2 - root causes

Three: Establish Consequences After the Top Event

Next we need to look at what the direct consequences of breaching the runway are. These consequences are the intermediary events before our Top Event and final Impacts, or damages. In our scenario, the direct consequences were:

  • Rolled onto the runway;
  • Reported in press; and
  • Terrified passengers.

It’s important to distinguish between consequences and Impacts. Consequences do not cause Impact damages themselves, but lead directly to damages.

Aviation Bowtie analysis step 3 - consequence events

Four: Establish All Consequences (Damages)

Impacts, also called "risks" and "consequences", are always characterized by damages. Damages could be to persons, equipment, reputation, money, etc. – anything that hurts your organization. Picking out damages is usually pretty easy.

Here are a few examples of Impacts in bowtie analysis:

  • Fines;
  • Loss of life;
  • Injury to persons;
  • Damage to aircraft or equipment;
  • Loss of aircraft or equipment;
  • Reputation damage;
  • Loss of stock value (financial loss); 
  • Reduced passenger revenue;
  • Reduced confidence in safety program by employees (safety culture); and
  • Possible litigation.

Each item in red causes an element of damage to the company.

Aviation Bowtie analysis step 4 - Impacts

Step 5: Insert Risk Controls Where Appropriate

The last step that is critical to bowtie analysis is to list your risk controls directly after each item to see how your risk controls failed. If you are unable to list a risk control, it’s a good indication that you need to implement one.

A few examples of risk controls are:

  • Preflight clearance checklist;
  • GPS;
  • Short field takeoff;
  • Compensation packages; and
  • PR Control.

This example is a bit limited by space, but in actual practice you will have more space to fit in your risk controls nicely. Moreover, your bowtie analysis will feature as many risk controls as possible, perhaps even several risk controls per item.

Aviation Bowtie Analysis step 5 - risk controls