Flight 148

Welcome to Flight 148 Imagine a January 20, 1992 from Lyon to Strasbourg ready to take off and at the moment the plane crashes and only 9 people survive, what would you think of a thing like this?

Read a bit of this story and tell your theory. The crew was late in modifying its approach strategy due to ambiguities in communication with air traffic control. They then let the controller guide them and relaxed their attention, particularly concerning their aircraft position awareness, and did not sufficiently anticipate preparing the aircraft configuration for landing.

In this situation, and because the controller's radar guidance did not place the aircraft in a position which allowed the pilot flying to align it before ANDLO, the crew was faced with a sudden workload peak in making necessary lateral corrections, preparing the aircraft configuration and initiating the descent.

The key event in the accident sequence was the start of aircraft descent at the distance required by the procedure but at an abnormally high vertical speed (3300 feet/min) instead of approx. 800 feet/min, and the crew failure to correct this abnormally high rate of descent.

The investigation did not determine, with certainty, the reason for this excessively high rate of descent. Of all the possible explanations it examined, the commission selected the following as seen most worthy of wider investigation and further preventive actions:

The rather probable assumptions of confusions in vertical modes (due either to the crew forgetting to change the trajectory reference or to incorrect execution of the change action) or of incorrect selection of the required value (for example, numerical value stipulated during briefing selected unintentionally) .

The highly unlikely possibility of a FCU failure (failure of the mode selection button or corruption of the target value the pilot selected on the FCU ahead of its use by the auto-pilot computer).

Regardless of which of these possibilities short-listed by the commission is considered, the accident was made possible by the crew's lack of noticing that the resulting vertical trajectory was incorrect, this being indicated, in particular, by a vertical speed approximately four times higher than the correct value, an abnormal nose-down attitude and an increase in speed along the trajectory.

The commission attributes this lack of perception by the crew to the following factors, mentioned in an order which in no way indicates priority:

Below-average crew performance characterized by a significant lack of cross-checks and checks on the outputs of actions delegated to automated systems. This lack is particularly obvious because of the failure to make a number of the announcements required by the operating manual and a lack of the height/range check called for as part of a VOR DME approach.

An ambiance in which there was only minimum communication between crew members;

The ergonomics of the vertical trajectory monitoring parameters display, adequate for normal situations but providing insufficient warning to a crew trapped in an erroneous mental representation;

A late change to the approach strategy caused by ambiguity in crew-ATC communication;

A relaxation of the crew's attention during radar guidance followed by an instantaneous peak workload which led them to concentrate on the horizontal position and the preparation of the aircraft configuration, delegating the vertical control entirely to the aircraft automatic systems;

During the approach alignment phase, the focusing of both crew members attention on the horizontal navigation and their lack of monitoring of the auto-pilot controlled vertical trajectory;

The absence of a GPWS and an appropriate doctrine for its use, which deprived the crew of a last chance of being warned of the gravity of the situation.

Moreover, notwithstanding the possibility of a FCU failure, the commission considers that the ergonomic design of the auto-pilot vertical modes controls could have contributed to the creation of the accident situation. It believes the design tends to increase the probability of certain errors in use, particularly during a heavy workload.

What do you think about this situation, what would be your theory? Thanks to The Aviation Safety Network we know more about this case.

Credits to The Aviation Safety Network