B. Below expectation behaviour – Unintentional mistakes and system errors
B.1. Unintentional mistakes
Fig. 3. Unintentional mistakes and system errors tree
This type of behaviour includes all other types of unintentional behaviours, which usually generates unsafe instances in the organisation. This could range widely from errors caused by the system, honest individual mistakes or behaviours that can be categorised as both.
B.1.1. Human errors
B.1.1.1. Unintentional human errors
Genuine, or unintentional mistakes are unavoidable as human errors in any organisation. Any human error can be subdivided into several different types of errors:
- Slip: Slips are often not overly dangerous as they are noticed quickly and usually do not lead to damage or injury.
- Lapse (omissions – something not done): These can be more dangerous as they often go unnoticed (example: forgetting to replace an o-ring). These are especially dangerous during maintenance, where the problem can stay unnoticed for some time.
- Mistake: a mistake happens when people that make a mistake think they are doing the right thing. They can be so sure of themselves that they will not see the facts that say otherwise. Example: Somebody is behind in his operational training, whilst the system has already been changed. His trained reaction, based on the old system parameters, can lead to a mistake.
| International Example: The controller gave a crossing clearance to a tow truck, forgetting he had also cleared an aircraft to land. The work of an air traffic controller is very much dependent on the mental gymnastics of his or her brain. This incident could have ended dramatically, were it not for the fact that the pilot of the approaching aircraft saw the tow crossing the runway and performed a missed approach, or go-around. Another safety barrier in the aviation chain worked as planned. VNA Example 1: Wrong flight path: ATC gave instruction: ‘Track direct MILIV’ to CPDLC. Flight crew then responded “UNABLE”. Afterwards, ATC observed the aircraft to have turned left of runway and inquired the flight crew. Then, ATC received the response “WILCO” through CPDLC. It turned out that the flight crew had mispressed the “UNABLE” button. VNA Example 2: On 27/10/2012, during landing & taxi at TSN Airport, Flight VN1173 HAN-SGN, the alert “ECAM ENG2 REVERSER FAULT” came on. Afterwards, Engine 2 was checked to still have safety lock unreleased on the HCU. Investigation afterwards found out that the technician servicing the aircraft forgot to release the safety lock due to fatigue and work overload. |
B.1.1.2. Personal routine mistakes
Personal routine mistakes are demonstrated when an individual have made the same errors in multiple instances – when the same errors are not made by others in similar situations.
Besides the employee’s personal reasons leading to their history of mistakes, this behaviour category can also be caused by incorrect training or inappropriate designation of role. This is further indicated in B.2.2.
International/Domestic Example: Passengers are requested to turn off mobile phones and FM receivers during take-offs, taxis and landings. However, some individual passengers still use their devices despite being reminded directly by flight attendants.
B.1.1.3. Group routine mistakes
Group routine mistakes are demonstrated when numerous individuals within the same division or department make the same mistake repeatedly, potentially causing safety risks. This can also be classified as a system induced mistake, as human errors are only partly at play in this behaviour category.
Group routine mistakes usually result in the whole team to be investigated regarding their working conditions, procedures and other environmental factors that may contribute to the repeated mistakes. Afterwards, if identified to be primarily system induced, the whole team may receive additional coaching on spotting errors, reporting activities and how to detect trends and investigate underlying causes of routine mistakes.
VNA Example 1: VN531/PVG-HAN, on 05/05 and 11/05 moved on the wrong runway at PVG airport (which was under renovation and changing runway names).The incident was determined that there had be changes on NOTAM but they were not updated on Jeppensen Airport, leading to the flight crew to commit the error. Afterwards, the airport map was updated.
VNA Example 2: On 12/2/2014, a baggage handler incorrectly transferred 28 pieces of luggage (442kg) to flight MI636 of SILKAIR. Previously, the same baggage handling division also incorrectly left 36 pieces of luggage (433kg) on flight CZ3038 of China Airlines.
VNA Example 3: In the 2015 safety management report of the technical-maintenance department, 4 incidents of accidental inflating of emergency boats during check-up were recorded. Investigations showed that technical staff were not careful during check-up and accidentally activated air tanks to inflate the boats.
