What does the SOP mean
A cautionary tale for those who use a 80kt call SOP:– what does the SOP mean?
As PF of an experienced two-captain crew on a positioning detail, flying alternate sectors with seat change, my response to a 80kt call was ‘No’ (my ASI was only 75).
Human nature engaged automatic enquiry mode – both pilots; there was a quick cross check of the other instrument panel in a vain hope of determining which ASI was in error and why – an impossible task with a dual system. Then there was realization that there was a standby ASI, which confirmed a mismatch, but this required significant mental effort as the airspeed was no longer 80 kts, thus all three ASIs had to be re-inspected.
At which time the dutiful PNF called V1 (his ASI), which was followed immediately by rotate; it was a light weight aircraft with a low V1/Vr. The flight was completed, but not without further event as the main ASI was linked to several functions and inhibits – flap/gear interlock for one.
The company SOP stated “call 80kts … , only reject the takeoff above 80kts for engine failure, fire … etc, etc”, nothing about what if the ASIs did not agree. The aircraft type had low-level alert inhibit at 80kts, thus it could be argued that much of the pre takeoff briefing re alerts was superfluous, as only important alerts would be given anyway. The important action for ASI mismatch (or failure) was overlooked; perhaps the SOP (those who wrote it) assumed that crews would stop. Interestingly, subsequent variants of the aircraft had EFIS airspeed which included an amber comparator, which if annunciated above 80kts, was ignored as there was a selectable alternate airspeed source from the ADC. The modern systems are not as fault free as some would expect, don’t assume anything – they just have other ways in which to fail.
Lessons learnt; check your SOPs to ensure that they are workable and cover foreseeable circumstances – what if. Ensure that SOPs consider human factors – the effect of surprise and shock of the event and the natural desire to find out why something has occurred.
The SOP must be practical; exactly how will crews determine that there is an error, what are the allowable limits bearing in mind that each crew may not view their ASIs simultaneously. Does it matter which ASI is in error – just that they don’t agree?
Specify the action required, ensure that this is trained for at the appropriate level – in this instance, if an RTO is required, this should be as a skilled, automatic response to stop i.e. if ASIs disagree at 80kt any call / comment is equivalent to stop? Or should we be ‘go’ minded as per the RTO training aid?
As this stage of the tale / considering SOPs, the process is getting very messy – ‘what ifs’, ‘buts’; so back to the risks, what exactly are the risks of stopping or continuing the takeoff.
In many modern aircraft, an ASI mismatch could be a relatively low risk event, but to be sure, we have to understand all of the ramifications. Then of course, we encounter situations involving masking tape over static ports and covers left on pitot tubes – but these failings require SOPs other than an 80kt call. Then if the 80kt check is not for the ASI, then exactly how do you check for incapacitation, or do you assume the non response (mic selected off) is instant death ??!!
An air safety report? No, far too embarrassed at the time, although later there was an unproductive discussion on SOP wording with the chief pilot on the theme of what if.