Form 1 NATIONAL RAILROAD ADJUSTMENT BOARD Award No. 11056
 SECOND DIVISION Docket No. 10611-I
 2-BN-I-MA-'86
 The Second Division consisted of the regular members and in
 addition Referee Jonathan Klein when award was rendered.

Parties to Dispute:

Dispute: Claim of Employes:

 1. That, in violation of the current agreements, Burlington Northern Railroad improperly changed the seniority date of Machinist Melvin J. Forcier.

 2. That accordingly, the Carrier be ordered to readjust Mr. Forcier's seniority back to the previous date of May 18, 1972, as it had existed for some ten years.

 FINDINGS:
The Second Division of the Adjustment Board, upon the whole record and all the evidence, finds that:

 The carrier or carriers and the employe or employes involved in this dispute are respectively carrier and employes within the meaning of the Railway Labor Act as approved June 21, 1934.

 This Division of the Adjustment Board has jurisdiction over the dispute involved herein.

The Claimant began his Machinist apprenticeship with the Carrier on July 2, 1970. At that time, until an Agreement was reached on May 17, 1972, the standard period of apprenticeship ran approximately four (4) years. The Agreement in effect when Claimant began his apprenticeship contained Rule 38 dealing with apprentices, of which subparagraph (i) stated:
Form 1 Award No. 11056
 Page 2 Docket No. 10611-I
 2-BN-I-MA-'86
 s
 On May 17, 1972, Carrier and a number of shop crafts, including the ,
 Machinists, entered into an Agreement modifying Rule 38, which Agreement ex
 pressly superceded any interpretation, understanding or practice under pre
 vious training Rules that conflicted with the new provisions of the Rule. The
 stated purpose of the May 17, 1972, Agreement was to establish a modern train
 ing program to insure an adequate supply of qualified journeymen Mechanics for
 the Carrier's future labor requirements. In an important provision of that
 Agreement, the training period for regular apprentices was reduced from four
 to three years based upon a designated number of days of actual work on re
 gular working days.

 The May 17, 1972, Agreement also "grandfathered-in" those apprentices who, like the Claimant, were already in service. In Rule 38(k), the new Agreement provided in pertinent part:


tus Change" from Claimant's personnel file. This document established the -
 fact that Claimant last worked as an apprentice on April 29, 1973, approxi
 mately three years after he began his apprenticeship with the Carrier. This
 document reflects the fact that the remainder of Claimant's training was chang
 ed to conform to the new three year apprenticeship period established under
 the May 17, 1972, Agreement. This document states in pertinent part:









Form 1 Award No. 11056
 Page 3 Docket No. 10611-I
 2-BN-I-MA-'86
 Claimant retained this seniority date of May 18, 1972, for approxi-
 mately ten (10) years. On December 2, 1981, the Claimant was transferred from
 the Carrier's round house facility in Grand Forks, North Dakota to its North
 town Diesel Shop at Minneapolis, Minnesota. In so doing, Claimant also trans
 ferred into a new seniority district and his seniority date was dove-tailed
 with the other Machinists on what is commonly referred to as the Twin Cities
 Seniority District.

 It remains unclear from the record as to the precise date in 1982 when employees within the Twin Cities Seniority District became aware of Claimant's seniority date. Claimant's May 18, 1972, seniority date was not included on the January 1, 1982, Seniority Roster for the Twin Cities District. In any event, a protest was made by another Machinist on the roster as to Claimant's seniority date. Both the Carrier and Organization agreed on the property that Claimant's seniority date should have been April 30, 1973, rather than May 18, 1972. This change in Claimant's seniority date would have lowered his ranking a minimum of four positions on the January 1, 1982, Twin Cities Seniority District Roster. Claimant has appealed to this Board the joint decision of the Carrier and Organization to change his seniority date.

 The Claimant's correct seniority date hinges on a specific provision of the May 17, 1972 Agreement, and the interpretation given that provision by the conduct of the parties.

 The parties negotiated an Agreement containing Rule 38, subparagraph (1). That provision, on its face, was designed to protect any apprentice who started his training before May 17, 1982, from receiving a lower position on the applicable seniority roster than apprentices who started training after that date. In assigning Claimant a seniority date immediately after the effective date of the May 17, 1972 Agreement, the parties acted in accordance with the terms of their own Agreement to insure that an apprentice who began his training on May 18, 1972, almost two full years after Claimant, would not " . . . result in any such apprentice [Claimant] starting lower on the mechanics' seniority roster than apprentices who started training after the date of this agreement . . . .' This Board is not empowered to alter the agreement reached by the parties on May 17, 1972, or the mutual, interpretation given the Agreement's provisions by both the Carrier and Organization.

 It should be noted that Claimant's seniority date of May 18, 1972, was in effect each year for almost a ten (10) year period. Even assuming, arguendo, that the correct seniority date was April 30, 1973, Claimant, the Carrier and the entire Machinists craft in the Dakota-Fargo Seniority District relied upon the agreed date of May 18, 1972, during the ensuing ten years for purposes of layoff, recall, bidding, etc. The Board finds that both the Carrier and Organization are estopped from changing this date, where their present interpretation of their own Agreement differs from their earlier interpretation given within one (1) year of the Agreement's effective date, and upon which the Claimant, Carrier and other Machinists relied for a period of approximately ten years. Third Division Award No. 21703 cited by the Carrier
 Form 1
 Page 4

 Claim sustained.

 Attest:

Dated at Chicago, Illinois, this 29th day of October 1986.

 Award No. 11056
 Docket No. 10611-I
 2-BN-I-MA-'86

 is inapposite to the facts of this Claim. Award No. 21703 represents a decision by the Third Division to reject interpretation of a Claim under the terms of a non-existent rule merely because the parties mutually misunderstood that Rule to have application to the facts of that case. Indeed, this Board itself would have to apply a non-existent Rule to confirm April 30, 1973, as Claimant's seniority date, and commit the very act condemned in Award No. 21703. This Board must respectfully decline to take such action. The Carrier and Organization are ordered to correct their records to reflect May 18, 1972, as Claimant's correct seniority date.

 A W A R D

 NATIONAL RAILROAD ADJUSTMENT BOARD
 By Order of Second Division