Some thoughts (from a pilot with a reasonably extensive professional design engineering and certification background) –
There are two sets of rules in play -
(a) Certification (eg FAR 25, ANO 101.5/101.6 and antecedents, now all long gone to the rules graveyard somewhere ..)
(b) Operations (eg FAR 121, CAO 20.7.1B)
plus ayres and minor variations in other codes.
It would be nice if both sets of rules in each of the various jurisdictions were neatly aligned but that is not always the case .. engineers and pilots don’t always think the same way and confusion sometimes is the result. CASA has some certification experienced engineering/pilot folk in the operations regulatory arena so, perhaps, we might see things progressively improve.
We have the historical baggage associated with older local requirements (now defunct – the old 101 series of Orders, especially those with many dot subordinate identifiers in the callout). All but the very much older folk (probably Leaddie, due to the performance engineering folk with whom he came in contact in his early airline years and, perhaps, Stallie) in the PPRuNe sandpit will have no knowledge/recollection of these at all. These long preceded 101.5/101.6, themselves also gone to the archives and, I daresay, most here will not have any recall of their content either.
For many years, especially in respect of 101.5/101.6, these local requirements modified either the US or UK rules in various ways and caused the Industry all sorts of nuisances (until Ron Yates' Report pushed the rule makers to change things somewhat and those local rules were binned). Then, to confuse matters, 20.7.1B purported to talk operational implementation of the certification bases, occasionally introducing disjoints along the way. Add to that the penchant of pilots to produce 101 answers for most questions and the scene is set for OWTs.
It might be useful to keep the two sets of rules a little separate .. if you want to consider certification, then talk FAR 25 (or whichever set might apply in the circumstances). Ideally, the operational rules would look to flying the aeroplane in a manner compatible with the certification basis rather than confusing pilots’ minds in respect of (occasionally incorrect/incompatible) certification detail.
I see various posters quoting liberally from the FARs. Be VERY careful when you do this other than in a generic and, preferably, qualified way. The certification rules have varied GREATLY over the years, in keeping with technological capability BUT one generally doesn’t see retrospective application of new rules. That is to say, if you are looking at Aeroplane ABC, then you MUST check the TCDS to determine what version of the rules applied to its design and certification and then talk that version of the rules rather than the current set. In general, it is not valid to infer that a revised or new rule (not applicable to the particular frozen design standards defined for the original design) will apply, or be relevant to, that particular aeroplane. It follows that the rules applicable to one aeroplane may be quite different in detail to those applicable to another. This is quite relevant to a discussion on scheduled speeds where rules and interpretation has varied somewhat over the years.
Several posts query exceeding V1 with the reject commenced immediately prior to V1 .. once you start the reject, regardless of the speed, there necessarily will be a short period of (reducing) continued acceleration before things get sorted out (ie the brakes are actually doing their thing in earnest) and the speed starts to reduce very rapidly. In the case of the idealised sudden engine failure reject, engine rundown characteristics, timing and sequence of crew actions, etc., are very relevant to this observation. Once the levers are closed, boards up, and brakes on full song, deceleration will be very high in most cases (those who flew the 727 with the nosewheel brakes option will know what I mean) .. but it does take a finite time for this all to occur. The 2 second delay introduced at FAR 25 A/L 42 (and ANO 101.6 A/L 62 if I recall correctly ?) provided some much-needed, if small, fat for pilot comfort and rational reality
For a normal (dry runway) reject, reverse is held in reserve .. in any case, by the time significant reverse is achieved, the brakes have done the bulk of the deed and reverse has the main benefit of adding noise to all the other excitement. On the other hand, in the case of a slippery runway surface, reverse might become very important to the pilot’s wish list.
The current “how it is done” description lies within FAR AC 25-7 which can be found at
https://www.faa.gov/documentLibrary/...2025-7C%20.pdf
Page 32 of this document indicates
Section 25.107(a)(2) was revised to remove the reference to “takeoff decision speed” from the definition of V1. V1 is the speed by which the pilot has already made the decision to reject the takeoff and has initiated the first action to stop the airplane … this should be taken to be the likely current FAA thoughts on V1.
Keep in mind, when reading the FARs, that one always has to read the applicable ACs to get the behind-the-scenes FAA story on what they thought the rules should mean.
If things go significantly awry, for whatever oddball reason (eg, in keeping with some concerns expressed in this thread - no brakes) and the certification boundary condition expectations cannot be met in reasonable measure, the whole thing then is very much in the lap of the Gods. Leaddie’s post #29 is pertinent.
A similar oddball case is the low speed (Vmcg-limited) V1 critical fail reject in the presence of a significant adverse crosswind .. continuing, with the aircraft out of control directionally, is not a good option and a post-scheduled V1 reject might be the way to go (ie stop). Another example is the airborne Vmc case where the pilot fails to apply the necessary bank inputs … and over we go. A read of the Darwin Braz mishap is useful, and sobering, for this one.
However, whatever the situation, if you are well outside the postulated certification parameters, then the performance capabilities of the aircraft on a critical runway probably aren’t going to give you a nice outcome ... if the initial OEI reject decision is reversed on a critical runway, the runway head speed probably isn’t going be useful. Sometimes we just have to accept that the Gods are mischievous on occasion and we might not make it home. Certainly, the certification rules don’t give guarantees .. only probabilities.
Keep in mind that the basic certification idea is a single major failure to contend with. Sure, historical reality tells us that the real world doesn’t always mirror the certification idealisations as nicely as we might like to see, but the further we get away from the test conditions .. the further we get away from a potentially happy outcome. Refer Aerocats’ #34.
Note the 3 second margin that's built into the V1 certification data. Refresh my memory as to the story here ?
2 seconds after you initiated braking and retarded the thrust levers you realise the brakes are not working. You are now over V1 and the engines are spooling down. You will be WELL over V1. What to do ? All depends on a heap of things which defy analysis in an instant on the fly. Retracting the gear/ground looping might be an option if all else appears to be covered in blood. If you have another 10,000 ft or so ahead, you may be having a somewhat better day. In any case, I doubt that one would take anything like two seconds to recognise a significant brake failure ...
What does concern me is the apparent thinking that all this is black and white. That just ain’t the case. The certification standards presume certain conditions etc. and, to be sure, generally those presumptions work out reasonably well in practice as we don’t have aircraft falling about us day in day out.
However, one should not lose sight of the fact that the certification performance rule book presumes an idealised, prescribed world – it has to do that if there is to be any repeatability in testing - albeit with a bit of fat here and there to provide some protection for innocents abroad. Now, if the real world on the day varies significantly from that postulated .. don’t be surprised if you don’t see the aeroplane match the book. If the delta is significant and not your way, then don’t be surprised to see tears at the end of the day.
The present Industry thought about V1 (viz., in general the outcome is far more likely to be happy if the takeoff is continued from V1) endeavours to incorporate real world, historical, statistical reality while generating cockpit simplicity for SOP. IT DOES NOT GUARANTEE a happy outcome ALL the time .. but, certainly, most of the time things will end well.
If, on the day, the boundary conditions vary significantly from those presumed, and were not amenable to pretakeoff planning (I'm sure we all do think about the what-ifs and how we might handle them ?) the Commander gets to earn his/her pay in a very short time .. win (hero/heroine), lose (scapegoat), or draw (lives to fly another day, albeit with sweaty palms at the time).
The thread discussion, however, is invaluable, as it encourages thinking and provides an opportunity for newchum education.
It has been my observation that the majority of endorsement courses and recurrent training probably don’t give enough detail to the details and the limitations .. which is why some of us, with a foot in both camps, have approached pilot training from a quite different starting point. Those of you who are fortunate enough to have very experienced ops engineers (especially those with significant heavy aircraft operational experience) associated with your operation and training are, indeed, most fortunate. Do heed their technical counsel.