First officer reports inability to maintain assigned altitude of FL430 due to OAT increase. ATC was ...

Narrative:

Prior to the event; cruise at FL400. Experienced continuous light with moderate turbulence. ATC inquiry into smoother altitude. Told FL410 and above smooth. Indicated that FL430 is not possible and offered FL410. Climbed to FL410. Later; just prior to incident; given a choice with respect to oncoming traffic to be at FL400 or FL430. Checked aircraft performance tables to determine that at current weight and temperature; cruise at FL430 was possible in either normal or long range cruise. Because of bumps; captain elected to go up to FL430. Aircraft performance was good in climb until reaching FL426 at which time performance began to degrade. Upon reaching FL430; the aircraft performance continued to worsen and a request was made to ATC for a block of 420 to 430. ATC said unable. Request to descend was made. ATC unable. Asked to make a turn in order to descend. Unable. Captain elected to not let aircraft performance degrade any further and began slow descent and told to tell ATC unable to maintain FL430. Told to maintain FL430; captain chose only option available and that was to descend very slowly after being given a turn. Both our aircraft and other aircraft reported each other in sight. Told the controller that we were clear of each other and already had gone by each other. Controller finally issued a clearance to descend. Our altitude at time of passing other aircraft was about FL426. It is important to note that aircraft performance showed ability to fly FL430; but the temperature inverted from minus 1 or 2 degrees below isa to plus 4 degrees isa. This change took place right at FL426. I know; because I was trying to trouble shoot why the aircraft would not hold FL430 when aircraft performance from manufacture showed it would. Looking back at the whole incident; I do not believe that the captain made any incorrect choices and that he did all possible to minimize the reduction in safety as a result of standard separation for the altitudes operating at.

Original NASA ASRS Text

Title: First Officer reports inability to maintain assigned altitude of FL430 due to OAT increase. ATC was unable to grant request for lower but slow descent is initiated to maintain flying speed; which resulted in a loss of separation.

Narrative: Prior to the event; cruise at FL400. Experienced continuous light with moderate turbulence. ATC inquiry into smoother altitude. Told FL410 and above smooth. Indicated that FL430 is not possible and offered FL410. Climbed to FL410. Later; just prior to incident; given a choice with respect to oncoming traffic to be at FL400 or FL430. Checked Aircraft Performance tables to determine that at current weight and temperature; cruise at FL430 was possible in either normal or long range cruise. Because of bumps; captain elected to go up to FL430. Aircraft performance was good in climb until reaching FL426 at which time performance began to degrade. Upon reaching FL430; the aircraft performance continued to worsen and a request was made to ATC for a block of 420 to 430. ATC said unable. Request to descend was made. ATC unable. Asked to make a turn in order to descend. Unable. Captain elected to not let aircraft performance degrade any further and began slow descent and told to tell ATC unable to maintain FL430. Told to maintain FL430; captain chose only option available and that was to descend very slowly after being given a turn. Both our aircraft and other aircraft reported each other in sight. Told the controller that we were clear of each other and already had gone by each other. Controller finally issued a clearance to descend. Our altitude at time of passing other aircraft was about FL426. It is important to note that aircraft performance showed ability to fly FL430; but the temperature inverted from minus 1 or 2 degrees below ISA to plus 4 degrees ISA. This change took place right at FL426. I know; because I was trying to trouble shoot why the aircraft would not hold FL430 when aircraft performance from manufacture showed it would. Looking back at the whole incident; I do not believe that the captain made any incorrect choices and that he did all possible to minimize the reduction in safety as a result of standard separation for the altitudes operating at.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	864999
Time
Date	200912
Local Time Of Day	1201-1800
Place
Locale Reference	ZFW.ARTCC
State Reference	TX
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 135
Flight Phase	Cruise Climb
Route In Use	Direct
Flight Plan	IFR
Aircraft 2
Make Model Name	EMB ERJ 135 ER&LR
Flight Phase	Cruise
Route In Use	Other Unknown
Flight Plan	IFR
Person 1
Function	Check Pilot First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 95 Flight Crew Total 11200 Flight Crew Type 1040
Events
Anomaly	Conflict Airborne Conflict Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Speed All Types
Miss Distance	Horizontal 7000 Vertical 1500

First officer reports inability to maintain assigned altitude of FL430 due to OAT increase. ATC was unable to grant request for lower but slow descent is initiated to maintain flying speed; which resulted in a loss of separation.