B777 EXCESSIVE CABIN PRESSURE LEAKAGE
Deniz Turan
Technical Instructor, B1/C Licensed Aircraft Maintenance Engineer A320, B737, B777, B787
Why do we pressurize an aircraft for maintenance on the ground?
The answer to this question should be to find for air leak location in the pressurized area of the aircraft.
This test requires a higher absolute pressure than the cabin pressure achieved during ordinary aircraft operations.
Since this test is an operation that requires safety and experience, the engineer in the cockpit must be trained and experienced. Other than these people, there should be no one on board the aircraft.
In addition, they must be in good physical condition. I would like to share the note about this in the B777 pressurization procedure.
‘’NOTE: People with a cold, ear ache, sinus problem, or other illness are not considered to be in good physical condition and should not be on the airplane during the test.’’
Serious health problems may occur due to the effect of pressure.
APU or pneumatic ground cart can be used for air source. It can be performed with APU according to B777 AMM procedure.
Pressurization is started by providing conditioned air with the cooling package.
领英推荐
OUTFLOW valve switches position are set to MAN, so OUTFLOW valves are controlled manually.
You must monitor the EICAS for the RATE-OF-CABIN-CHANGE display during this time.
This rate is very important.
When increasing pressure, do not increase more than 1000 feet per minute. If you do this, you may cause damage to the aircraft structure or injury to persons.
When the desired difference reaches the value of approximately 4 psi, turn off the pack switches. Thus, the pressurized air will remain in the cabin and will not be pressurized any further. In the meantime, you can check for air leaks.
I have a question regarding this subject. On an undesirable scenario.
What can be done as an authorized aircraft engineer on ground when the engineers in the cockpit lose consciousness and lose communication during pressurization?
If you know the answer to this, can you write it in the comments?
Thank you
Technical Instructor at Queensland Aerospace College
9 个月Another safety solution to this scenario is to always have a minimum of 2 trained engineers on board during these type of tests. Thus if one suffers from the high pressure condition, another person can take over the procedure and depressurise the aircraft to obtain assistance for the injured person.
Licensed Aircraft Certifying Engineer - CAT B1
10 个月Deniz Turan Thanks for sharing the experience and info. In case of incapacitation, we may just release the cargo door handle to open up the small flap door on it to release the pressure from the cabin without unlatching / unlocking the cargo door…. ??????