777 Fragen und Antworten

[Simeon S]

Nachdem ich die 777 einige Zeit geflogen bin, "quälten" mich dennoch einige Fragen. Diese wollte ich auch nicht von PMDG beantwortet haben, sondern ganz objektiv von jemanden, der sich auskennt. Dafür habe ich einen 777 Piloten gesucht und gefunden. Vielleicht hat sich der eine oder andere eine der Fragen auch schon gestellt und deshalb möchte ich Euch die Antworten weitergeben. Ich habe nicht nach speziellen Situationen und Precedures gefragt, sondern nach der allgemeinen Situation des normalen täglichen Linienfluges.

Which T/O and climb thrust mode do you usually use?

Take off and climb thrust is dependant on the take off profile. This is determined by numerous factors. Some of these are dictated more by company procedure and philosophy than anything else. For instance, because this aircraft is so powerful there are instances when it is not necessary to use maximum available thrust for take off. This is determined by such factors as runway length, field altitude and aircraft weight. By not using maximum thrust for every take off the engines are, therefore, not stressed every take off. By doing this the life of the engines is significantly extended, a major economic benefit. The selection of a reduced thrust take off can affect the computed climb thrust. So, in order to utilize the best efficiency we generally take off with the VNAV function armed. It becomes active at about 400 ft AGL. From that point on it switches from TOGA ( take off/ go around) mode to the computed VNAV profile. This is enunciated as green VNAV and THRUST REF. THRUST REF refers to the computed thrust required to maintain the climb profile/ climb speed.


If you climb in VNAV with clb as thrust ref, what is the approx. vertical speed between FL200 and FL300?

Again the climb performance, particularly in the FL 200 and Above is determined by several factors. The most salient is aircraft weight. However, in general you could maintain from 2000 fpm at FL 200 to 1000 fpm at FL 300. If the aircraft took of at max gross weight this performance is likely to be less than if the aircraft took off at some weight less than maximum.


If you fly with the VNAV mode and you have a complete flightplan entered in the FMC - do you still have to tune in every altitude at the MCP manually?

Yes. the system is designed to maintain a safe or last cleared altitude. The system is designed in such a way that once you reach a selected altitude it is possible to preselect the next altitude you expect in the profile. With VNAV engaged the aircraft will begin a descent to that selected altitude once it reaches the computed top of decent point. From a practical stand point, however, It is generally accepted practice to NOT select an altitude in the MCP until air traffic control issues a clearance to change altitude. This is a safety procedure which reduces the probability of violating an altitude clearance.

I'm also interested in the speed and deceleration behavior on approach. Is it hard to slow down the A/C to maybe 190 kts from 240 in order to prepare for final approach? Du you have to use the air brakes and if yes only half or full deployed to reduce speed?

All modern jet transports have the problem of slowing down. This is due to their clean and efficient aerodynamic design and the large fan engines. In one case the aircraft takes relatively little power to maintain speed. That is why these aircraft are so economically desirable. And the other is the fan engines produce a significant amount of residual thrust even at flight idle power settings. As you have noticed, this makes slowing down an evolution which requires some planning. The process is generally accomplished by slowing the aircraft incrementally based on the maximum flap extend speeds. In the real world in order to not damage the flap system we slow the aircraft to 10 kts below max speed for the flap setting then select that flap setting increasing the drag. For instance lets assume the max speed for Flaps 1 is 245kts. we slow to 235kts and then select flaps to 1. This gives us a 10kt gust buffer. When it is necessary to slow more precipitously then by all means use the speed brakes, and when you need to slow even quicker you can lower the landing gear, that will give you max drag thus max deceleration.





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