PNF-commands?

[Guest frankathl]

Hi Susan,"But I realy don`t understand that even the V1 call-out can be left nowadays: I thought that the PF has to watch only at the RWY until the plane has finished to rotate and positiv V-SPeed has been confirmed by the PNF! So until that point the PF realy has no time to look down to check V1, doesn`t he?"Yes, you are right, you would normally expect to hear the V1 call. In some cases, though, the V1 and VR speeds are quite close to each other and, since the call to "Rotate" is made at VR minus 5 knots(to give the PNF time to make the call without passing VR), it can happen that the timing of the V1 call and the "Rotate" call coincide. In such circumstances, since the aircraft has by now reached rotation speed, the "Rotate" call takes precedence. I think this is what happened in this situation(I need to go check if the V1/VR speeds are mentioned on the tape). "That leads to another question: Does the PF "feels" the braking actions of the *Autobreaks* (Mode 1 or 2) with his feet on the pedals? Or is it that way that there is no pressure/vibration at the pedals (that can be felt) when the plane is autobraking until that moment the pilots switch autobrake off and use the brakes (pedals) manually?"I don't think there is any particular "feel" through the pedals, although the effect of the braking action will, of course, be experienced through the entire aircraft structure, which may well result in some vibration being felt. If you're asking if the pilot senses when to apply manual brakes through some kind of feedback from the autobrake system, I think the answer is "No". Rather, the effectiveness of the autobrake system is determined by monitoring aircraft deceleration and, in the normal case, applying manual brakes when the plane has slowed to a pre-determined speed. This speed varies with runway condition and stopping requirements, but is normally about 80 knots. To quote the manual:"The aircraft speed at which the transition from autobrake ot manual braking is made varies with aircraft deceleration and stopping requirements. For runway conditions that produce good deceleration, the transition from autobrake to manual brakes should be made at about 80 knots. The transition speed should be closer to a safe taxi speed on very slippery runways, or when runway length is limited."The autobrake system will disarm as soon as pressure is applied to the manual brakes(Note, by the way, that full manual braking produces a greater deceleration rate than the autobrakes operating with the MAX setting).BR,Frank

[Guest Cantuezel]

Thanks again for your answers, Frank.>...>Yes, you are right, you would normally expect to hear the V1 call. >In some cases, though, the V1 and VR speeds are quite close to each >other and, since the call to "Rotate" is made at VR minus 5 knots(to give the PNF time to make the call without passing VR)... >...Well a "stupid" question: Would it be "bad" if the PF would announce rotate at the very rotate speed, the PF would have to react then and the plane would (realy) rotate at VR+ 5-10...? I mean it cannot be bad if the a/c rotates at even greater speeds than predicted, doesn`t it? :)GreetingsSusan

[Guest ChrisY]

It would not be a good idea Susan. This is because you would have travelled further down the runway before getting airborne and your obstacle clearance would be compromised in the first sector of the climb especially if you had an engine failure after take off. On critical performance limited runways you may not clear obstacles. The call is made early so that you can rotate at the correct speed (VR). Deviation from this erodes your safety margins.ChrisY737 Driver since 1980