Trash Hauler,
My 'aliases' do not include the person named as Ground Engineer Number One in the Tsolakis Report, and whose “extensive tests” reported by Helios/Ajet will be detailed below.
As for your comment regarding cabin altitude rate of climb reaching 2,000-2,500 ft/min without noticeable discomfort, human physiology (say, of the eardrums) is not known to differentiate between ascent and descent – only between rates of change of atmospheric pressure. Therefore your comment about descent effectively supports the logical assumption that the discomfort (especially with 25 children on board) would indeed be very noticeable at a much earlier stage of the takeoff than FL120 when the Horn started beeping.
Gonzo,
Thank you for your constructive posts on this thread. Your query about the actual tests conducted by Helios is answered below. The text reflects the OFFICIAL position of the Cypriot company, as well as that of several Greek and British pilots, engineers and accident investigators whose names are withheld by request:
There is deep concern in Cyprus and Greece about the Report scenario being founded on the single assumption that the engineer left the pressurisation mode selector in MANual with the outflow valve at about 14.6° from the closed position. Total travel from fully open to fully closed is 110°.
The evidence presented by Chief Investigator Akrivos Tsolakis suggests that the bleeds were on throughout the flight and that the aircraft only partially pressurised to a 1 psi differential because the outflow valve was at about 14.6° from the closed position.
The argument is about not whether but at what stage this became the situation.
The assumption in the AAIASB Report is that it was at the end of the maintenance procedure, due to the alleged omission of the ground engineers to switch the Pressurisation Mode Selector back to AUTO.
However there are convincing arguments and empirical evidence that this is unlikely and that for reason or reasons yet unknown it occurred after takeoff but likely before the cabin altitude reached 10,000 ft.
The first point is that the captain and the first officer must each have made serious errors of omission during their independent preflight check of different components of the pressurisation system; the captain by not checking that the main outflow valve was fully open and the first officer by not checking that the mode selector was in AUTO.
They must then both have missed the abnormalities on the pressurisation panel during the various challenge and response checklist actioned before and after take off.
The engineer who did the maintenance, Mr Alan Irwin, (named Ground Engineer Number One in the Report), contested this scenario when interviewed in the UK by British aviation experts and his comments on the Report were considered and formally submitted to the AAIASB by the UK Air Accidents Investigation Branch (AAIB) itself.
One comment related to the significant pressure fluctuations that would occur during the aircraft start sequence if the mode selector was in Manual and the OFV about 14.6° from closed. The validity of the submission was verified by a competent UK AAIB engineer before it was sent to AAIASB for consideration.
To reinforce the engineer’s submission a practical test was devised by Mr Irwin in Britain. The UK AAIB declined to attend as they were satisfied that the written report he had submitted through their office accurately reflected the situation, consequently they did not require empirical proof.
Reassurance was given by the Greek AAIASB in July that the engineer’s comments on the Preliminary Report would be appended to the Final Report if no agreement could be reached. Although this is required by ICAO Annex 13 and - more importantly - by Greek Law, it was not done. Helios/Ajet’s comments were also not appended.
The tests conducted and incorporated in Mr Irwin’s submission to the AAIASB confirmed the following:
Under normal circumstances, there are no significant fluctuations of cabin pressure while the aircraft is on the ground because the selector is at AUTOmatic and the OFV is driven fully open. Even when all the doors are closed this is sufficient to keep the cabin at the same pressure as the outside world.
The AAIASB Report assumes that the selector was in MANual and the OFV about 14.6° from closed when the flight crew started their various preflight preparations.
In this condition, air is fed into the cabin and escapes through the various open doors and apertures, a relatively small amount also escaping through the almost closed OFV. The differential between the cabin and the outside world would remain at zero.
When the passengers are on board and the last door is closed, the air can only escape through the partially closed OFV and natural leakage points. The aircraft starts to pressurise immediately. All the aircraft occupants would immediately feel the effect on their ears and the attention of the flight crew would be drawn naturally to the pressurisation panel by this abnormal situation.
Immediately before engine start, the air supply to the cabin is switched off and it would start to depressurise immediately. All the aircraft occupants would again feel the effect on their ears and the attention of the flight crew would be drawn naturally to the pressurisation panel by this abnormal situation.
After the engines are started, the air supply to the cabin is reinstated. The cabin would start to pressurise immediately. All the aircraft occupants would feel the effect on their ears and the attention of the flight crew would be drawn naturally to the pressurisation panel by this abnormal situation.
These three significant fluctuations of pressure during this period would be abnormal and evident to all occupants of the aircraft and there significance would be obvious to the flight crew.
Pilots are very aware that it is very important that the aircraft is not pressurised for take off, or landing. If the aircraft is pressurised and an emergency occurs on the ground that required an aircraft evacuation, it would not be possible to open the doors and hatches to allow the occupants to escape.
The long string of ostensibly co-incidental omissions by the flight crew and the abnormal pressure fluctuations during the engine start sequence are compelling evidence that the selector would not have been in MANual with the OFV 14.54° from closed when the flight crew arrived at the aircraft.
The point made about a cabin rate of climb of 2,500 feet per minute being noticeable is valid in its own right, regardless of the preceding implausible situation on the ground. While the aircraft climbs at up to 3,000 fpm to its cruise altitude, the cabin being pressurised only has to climb to about 8,000 feet so climbs at a much lower rate, 500 to 700 fpm. This is comfortable to the occupants and is not normally noticeable with unbearable discomfort. The rapid pressure changes experienced in a climb at 2,000-2,500 fpm would be very noticeable even for the experienced flight crew.
Conclusion
The accident scenario in Final Report depends entirely on the assumption that the pressurisation mode selector was left at MANual, with the outflow valve at about 14.6° from closed, after the unscheduled maintenance procedure earlier that morning. Although there is circumstantial evidence that the system was in manual from shortly after take off , there is no firm evidence to support the theory that it was left in MANual by the engineer.
The Report does not consider any alternative scenario.
Therefore if the Board accepted the statement by the engineer that he left the selector in AUTOmatic and considered the comments on the Draft Report by both the engineer and Helios/Ajet that supported this, the Board would have been obliged to reopen the investigation and start again, as the whole accident scenario was based on this single assumption.