alf5071h,
Definitely some important points to consider. For discussion:
Although the lack of reverse was in the briefing, the exact procedure was not discussed which deprived the handling pilot opportunity to visualise his intended actions (recall and refresh from memory), and for the monitoring pilot to both understand the ‘plan’ (what he would be monitoring) and an opportunity to interject if the briefed procedure was incorrect.
Unless we are looking at different documents there was no briefing included in the CVR Transcript. It starts 30 minutes prior to the event with the Captain's PA to the passengers. There is a 22 minute gap from 18:22:39-18:43:04, but it has to be assumed that this because there was nothing pertinent recorded in this interval. Quite possibly the briefing took place just prior to the PA, which is often the case, and was either no longer on the recording or has not been released for some reason.
The possibility that neither crew member knew of the revised procedure remains open, but they had landed in this configuration previously – what procedure was used then?
The FDR data for the previous landing at Porto Allegre shows that the movement of the 2 TL's was synchronous from CLB to IDLE to REV IDLE to MAX REV and back to IDLE. I believe that it has been established that this landing was accomplished by the same crew with the other pilot handling the aircraft.
Post#1893 reports an earlier A320 incident; considering the previous ATR incident and an earlier excursion with a 737, then the indications of this operation was one of high risk. ...
So why didn’t the 737 overrun (or previous ATR, F100 incidents) ring the safety alarm bells, trigger a risk assessment and the reconsideration of operations during the temporary conditions affecting the runway?
How do we know that the bells weren't rung in some quarters? Is it possible that factors other than changes to the runway surface condition were present in the other two incidents (as is the case here) and were quickly determined to have been the deciding factors in those incidents? If so a decision to continue normal operations may not have been unreasonable. How many pilot reports regarding low runway friction were received prior to the event and how were those investigated?
Why did the TAM overrun generate 1900+ PPrune posts vs 11 for the 737?
Well, of course there is the "sensational" aspect which attracts a great degree of attention, but the other reason why this accident is generating so many posts is the unusual amount of factual data that has been released publically in advance of the completed investigation. That amount of data is not available with respect to the other incidents so there is nothing there for qualified observers to consider. In the case of the B737 there's a picture of where the aircraft ended up, but very little information about how it actually got there.
Are we misjudging the important aspects of safety, being biased by fatalities, or incorrectly focussing on the ‘bright’ or emotive aspects of automation?
Of course we are. Public (as in where there is the attention of the general population as opposed to just industry professionals) attention is always biased towards the tragic results of a process gone wrong and not the indicators of risk that a process is going wrong that appear before the tragic result. That is human nature, but it doesn't preclude that there may have been significant discussions occuring pre-event among the professionals involved in operations at CGH. What those discussions may have been and what conclusions may have been drawn would certainly add a great deal to the discussion here. So far though, aside from a few generally attributed "A XXX pilot said this ...", there has been no real reporting of what was happening at CGH prior to the accident.
I would agree that the focus on
"the ‘bright’ or emotive aspects of automation" is for the most part a misplaced one that seems mostly to have been introduced by observers who don't have personal knowledge of the automation. How the automation works in practice for someone trained in its use versus how the automation is supposed by someone who has no experience with it in reality are two very different things, and that split is clearly shown by the difference in comments here between those who have that experience and those that don't.
The risk assessment reflected in this thread appears to be biased, if true then is this due to a failure in our beliefs, knowledge, training, safety management culture or just another facet of human behaviour?
Perhaps so. Each of our backgrounds biases the direction from where we perceive the greatest risk might have been. For bubbers et al it's clearly simply in flying an Airbus with non-moving thrust levers. For others it relates primarily to the runway length and condition, and some like yourself see the MEL’ed reverse and associated procedure as having a higher level of precedence in the chain of causation. My interpretation of the information available leads in the direction of the braking procedures being a key link in the risk assessment chain.
In a previous post you said:
With hindsight the aircraft should not have made the approach due the combination of runway / airport conditions and aircraft configuration. Thus a conclusion could be that there was a failure in risk assessment.
Personally, I don't think that this case has been made as of yet. To me, the degree to which the availability of the TR's is relevant to the decision is directly related to the degree of certainty that the crew
believed they had in the condition of the runway. The TR's don't factor into the aircraft's assessed stopping capability though they do provide an increased margin against limiting conditions. Suggesting that the go/no-go decision should have been made with the availibility of reverse as a primary basis of consideration would be to suggest that the current regulated operating margins are insufficient. Perhaps that is true, but if it is I think it would be a bit unfair to assess a failure of adequate judgement to the crew (as opposed to the manufacturer/regulator/operator) for not demanding a higher margin than regulations require.
To me, a key point in the land/divert judgement was the crew's assessment of the runway condition based on the available information. How often is CGH reported as "wet and slippery" and what meaning did those words have from the crew's perspective? Experience biases our judgement and a man who has done many landings at CGH, and likely received many "wet and slippery" reports there, has probably built a particular model of stopping performance expectations. We'll never know for this particular crew, but important related questions that I see are:
- What level of degradation in performance do pilots at CGH practically associate with a "wet and slippery" report and how does that align with the reference values of "wet" in use to determine the aircraft's capability? If they typically associate this with lower performance than "wet" then there's a clear indication of a risk not adequately assessed by the operator as well as the crews.
- What was the actual friction coefficient at the time and how well did it align with the "wet and slippery" report issued by the tower? Does "wet and slippery" have the same meaning for the issuers of the report as it does for the recipients?
- How much effect did the resurfacing work have on braking conditions and how well was this reflected in modifications to braking action conditions reported by the tower or assessed by pilots?
- Overall, what level of confidence did the pilots have in correlating runway condition reported to actual braking action experienced?
If the pilots had a high degree of certainty about the stopping action they expected and that that level was within the documented safe range for operating the aircraft, then I don't think the aircraft condition with respect to reverse plays much of a factor. However, if the opposite is true, that the pilots had a lowered level of confidence about the stopping action, then I would agree that the aircraft configuration with respect to reverse becomes a key consideration in the risk assessment and decision making process that took place prior to the landing.
Much has been said about landing distances, but how often do crews assess their landings against the requirements? Do crews routinely assess if the aircraft was capable of stopping within the safety margins provided for a limiting runway? Do crews check what % of max landing weight they are at, or how much additional runway they have/have not for a normal landing? Most landings are made on non limiting runways thus crews have few references as to how close they were to the required limiting performance, particularly in less than ideal conditions.
This is, in my opinion, an critical set of questions. The answers in this case might tell us alot about the delay in the application of manual braking on landing. The basic performance data available makes it clear that landing at CGH in wet conditions is an operation that approaches the limits of the aircraft's performance, and the pilot's decision to go below the G/S to achieve an early touchdown supports that he was aware of that fact. So, why then did he consider it acceptable to wait for confirmation of autobraking as opposed to considering it neccessary to apply manual braking right from the moment of touchdown?
I don't mean this to imply criticism of the pilot specifically, it may have more to do with manufacturer or company training or standard procedures, but if there's a clear failure of risk assessment evident in the information so far available it is the failure to appreciate the importance of ensuring (not assuming) immediate braking on landing when operating into a runway which is close to the limiting conditions of the day.
Researching what printed guidance there was on the subject I came up with the following from the Airbus FCTM (02.160 P6-8):
BRAKES
The use of auto brake versus pedal braking should observe the following guidelines:
- The use of A/BRAKE is usually preferable because it minimizes the number of application of brake and thus reduces brake wear. Additionally, the A/BRAKE provides a symmetrical brake pressure application which ensures an equal braking effect on both main landing gear wheels on wet or evenly contaminated runway. More particularly, the A/BRAKE is recommended on short, wet, contaminated runway, in poor visibility conditions and in Auto land. The use of LO auto brake should be preferred on long and dry runways whereas the use of MED auto brake should be preferred for short or contaminated runways. The use of MAX auto brake is not recommended.
- On very short runways, the use of pedal braking is to be envisaged since the pilot may apply full pedal braking with no delay after touch down.
So, questions from this might be:
- How much of this advice makes into line training?
- What differentiates a very short runway from a short runway?
- Did TAM make this distinction with regard to CGH?
- What if any training occurs to help aid the pilot in making the distinction when conditions vary?
It seems from the FDR data available that immediate manual braking in itself would not have prevent the accident when the thrust component of engine 2 is considered, but it would have changed the dynamics of the overrun significantly. As others have calculated previously, with maximum manual braking from just after touchdown the overrun would have been at a significantly lower speed given the actual deceleration rate experienced when the brakes were fully applied. And, depending on what level of reduced braking coefficient is ascribed to the runway condition it is possible that a stop on the runway could still have occurred had the runway been dry.
ELAC