however it is there as an aid not to rely on
Increasingly, this has ceased to be the case. Today, the automatics are relied upon, all too often, blindly.
Firstly, a 'war-ie', which I've probably told before here on Pprune.
Some years ago, I was doing my annual line check (in a B777), Dubai to Jeddah, (a nice day sector without any real traps for young players). It was my leg outbound and the FO, an Australian, who was ex-GA, was also doing his line check and would fly the return sector.
The aircraft had been written up repeatedly for double FMS failures, and sure enough, we had one in the cruise. For those not familiar with the triple 7, a dual FMS failure, except perhaps during a complicated SID or STAR, is a relatively no sweat problem. Even with both systems failed, you're still left with the three most important pages of the FMS immediately available to you, if with slightly reduced user friendliness.
(For instance, you – [gasp!] have to actually tune the navaid!)
Recovering the system to full operational capacity is also usually a relatively simple procedure, so it wasn't as if we felt we were suddenly doing a sim. ride. Following the recovery procedure, we got both systems back on line, so we proceeded normally to destination. I briefed for the approach, but since I knew there was a chance the FMSs might spit the dummy again, and since I knew my FO would be comfortable with flying basic instruments, I went to some lengths to include in my briefing that if the FMSs failed again below 15,000’, we would not try to recover them, but switch the nav display to the old fashioned CDI display and follow the VOR radial in until we were put on radar vectors. Part of this ‘belts and braces’ approach to our approach included manually tuning both the ILS and the VOR and both of us pre-setting the required VOR radial on our individual FMSs. This meant, if the FMSs failed again, all we had to do was simply rotate one switch each to give us the displays we would require.
Halas! Problem solved! We could get on with flying the aeroplane.
Are you finding this long-winded? I’m spelling it all out like this because I went into similar detail in briefing my FO (who I knew quite well and who I knew to be more than capable of handling any such downgrade) and the check captain.
You guessed it. I forget exactly when, but below 15,000’ on descent, both FMSs went west again. The FO and I did as briefed, switched to VOR display and went on with the descent, both quite comfortable with a CDI nav display both of us would once have thought as pure loooxury.
However, the check captain, who had sat through my detailed briefing without comment, was horrified. He had gone straight from his basic training into the right seat of a jet in his national flag carrier airline, (the national airline of the country that’s currently playing cricket against Ricky P. and his lads), and even in day and VMC, was not at all comfortable with the unfamiliar display.
“You can’t do an approach with a magenta line!” he cried, and proceeded to lean over the centre console and fiddle with the FMS until, at around 7,000’, (by which time we were on radar vectors and didn’t need it), he recovered that oh so necessary magenta line.
The check captain was (and remains) an above average captain. (He must be; he’s part of the check and training staff.) But he’s like an increasingly large proportion of airline pilots today. He has come to rely upon aids that, when push comes to shove, we all should be able to do without.
Too many of us today cannot.
---
Secondly, I watched ‘Air Crash Investigation’ recently, the episode about the Adam Air B737-400 that was lost when the crew switched their malfunctioning IRSs to ‘ATT’ mode after the NAV mode went off the rails. (A recurring problem on that particular aircraft, which was fixed – repeatedly – with a re-racking of the IRS and a squirt of WD40.)
Making this switching requires that the aircraft be flown straight and level for 30 seconds while the ATT mode sorts itself out. In IMC, at night and in stormy conditions, the captain was unable to do so. 30 seconds on the standby instruments, which includes a perfectly serviceable attitude indicator. That’s all it took – (that’s if he even looked at them!) – for a trained airline captain to put an aircraft full of people into a spiral dive.
The accountants will tell you – in their eyes, quite correctly – that the statistical chances of a double IRS failure occurring (or being induced by crew action) again (or in the first place!) during a period of extreme weather that would lead to the crew losing control during the switchover to ATT mode are so slim that the costs of training and maintaining the crews at a sufficient level of manipulative skills would far outweigh the loss of an airframe every ‘n’ thousand cycles.
Try telling that to the families, both of the crew and of the passengers on that Adam Air flight.