Thrust reversal - PRINCIPLES OF OPERATION

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Fig. 15-2 Methods of thrust reversal.

6. There are several methods of obtaining reverse thrust on turbo-jet engines; three of these are shown in  fig.  15-2  and  explained  in  the  following paragraphs.
7. One method uses clamshell-type deflector doors to reverse the exhaust gas stream and a second uses a target system with external type doors to do the same thing.  The third method used on fan engines utilizes blocker doors to reverse the cold stream airflow.
8. Methods of reverse thrust selection and the safety  features  incorporated  in  each  system described are basically the same. A reverse thrust lever in the crew compartment is used to select reverse thrust; the lever cannot be moved to the reverse thrust position unless the engine is running at a low power setting, and the engine cannot be opened up to a high power setting if the reverser fails to move into the full reverse thrust position. Should the operating pressure fall or fail, a mechanical lock holds the reverser in the forward thrust position; this lock  cannot  be  removed  until  the  pressure  is restored. Operation of the thrust reverser system is indicated in the crew compartment by a series of lights.