Plaintiffs argue that seven of the foregoing actions by the trial court were erroneous. Though not argued in that order, we consider first the actions complained of that relate to the trial as it was conducted — severing and trying first the claim against defendant Ward for negligence in piloting the airplane; refusing to receive evidence that the plane’s stall warning horn was not functioning; and instructing the jury on the sudden emergency doctrine. Neither of these actions was reversible error in our opinion and plaintiffs’ arguments in regard to them are overruled for the reasons hereafter stated.
*417I.
[1] Since Rule 42(b), N.C. Rules of Civil Procedure, authorizes a trial judge to order a separate trial of any claim or issue “in furtherance of convenience or to avoid prejudice,” the severance of the claim against Ward was within the court’s discretion, Aetna Insurance Company v. Carroll’s Transfer, Inc., 14 N.C. App. 481, 188 S.E.2d 612 (1972), and was not error since sound grounds therefor existed. White v. White, 312 N.C. 770, 324 S.E.2d 829 (1985). The claim against Ward aro.se from circumstances totally different from those that gave rise to the other claims involved and trying the pilot error issue separately was a comparatively simple process that had the advantage of possibly making it unnecessary to try the other issues. In re Will of Hester, 320 N.C. 738, 360 S.E.2d 801, reh’g denied, 321 N.C. 300, 362 S.E.2d 780 (1987). On the other hand trying the issue of Ward’s negligence in piloting the airplane with issues concerning Wilkins’ maintenance of the plane, an earlier induction system fire allegedly caused by the plane’s last user, and the personal liability of defendants Wilkins, Hicks and Toms because of their involvement with the nonprofit corporation that owned the plane would have been a cumbersome, complicated, and possibly confusing process that could have easily prejudiced one or more of the parties.
[2] The evidence concerning the stall warning horn not working and Wilkins’ failure to warn Ward about it was properly rejected because it was irrelevant to the only issue being tried — defendant Ward’s negligence in handling the airplane after the engine suddenly failed. Plaintiffs’ argument that the evidence should have been received since defendant Ward had alleged in his cross-claim against defendant Wilkins that Wilkins knew the stall warning horn did not work and did not inform him about it cannot be accepted. Plaintiffs had not charged defendant Ward with any duty or fault in maintaining or inspecting the airplane; they alleged only that he did not pilot the airplane properly after the engine failed; and they stipulated in the pre-trial order that “his routine preflight inspection of the aircraft . . . gave no indication of any problem with the airplane or engine.” Thus, when proffered the evidence was clearly irrelevant to the claim against Ward, and plaintiffs made no effort to make it relevant by moving for permission to allege that Ward was negligent either in inspecting or maintaining the airplane.
*418 [3] And since the evidence tended to show that a sudden emergency arose when the aircraft’s only engine failed without warning while taking off, the instruction on that doctrine was not error. Schloss v. Hallman, 255 N.C. 686, 122 S.E.2d 513 (1961).
II.
The other four court rulings that plaintiffs challenge are the dismissal of their claim against defendants Wilkins, Hicks, Toms, and Toms & Bazzle, P.A. for negligently causing the induction system fire; the dismissal of their claim against Wilkins for negligently maintaining the plane; the denial of their motion to set aside the corporate status of Mountain Scenic Aero, Inc.; and refusing to sanction defendant Wilkins for altering the physical evidence upon which plaintiffs’ case depended. Plaintiffs also assigned as error the dismissal of the claim against defendants Toms and Toms & Bazzle, P.A. in the separate action for failing to maintain liability insurance on the plane but since that point is not argued in their brief it is deemed to have been abandoned. Rule 28(b)(5), N.C. Rules of Appellate Procedure.
First, as to the dismissal by summary judgment of plaintiffs’ claim against defendants Wilkins, Hicks and Toms, individually and collectively, for negligently causing the induction system fire that allegedly led to the fatal crash: In supporting their motions for summary judgment these defendants did not contest the soundness of plaintiffs’ theory on this claim — that the last user of the plane by trying to start the engine with the fuel selector valve in the off position caused an induction system fire that damaged the carburetor floats and caused them to block the flow of gasoline when the aircraft was heading upward. All that they sought to establish, by affidavits submitted by each defendant, was that plaintiffs cannot prove that either of them knew about or was responsible for the induction system fire. Each affidavit was to the effect that the affiant had no knowledge of any fire having occurred in any part of the plane before the accident occurred. Plaintiffs opposed this showing with affidavits by Tedd L. Bishop, a retired military pilot who served as plaintiffs’ accident investigator, and Hugh A. Clark, II, who had flown in the aircraft less than two weeks prior to the crash. Based upon his inspection of the wreckage and photographs of the engine, Bishop opined that the engine failure came about as a “result of damage to the carburetor floats most probably caused, in turn, by an induction system fire which oc*419curred during a prior unsuccessful starting attempt by another pilot.” Clark stated that he flew with defendant Wilkins and Irvin Bazzle, the other attorney in Toms & Bazzle, P.A., on 4 June 1985 and that the aircraft was taxied directly back to the hangar rather than to the fuel pumps, as was usually done prior to hangar-ing. Other materials of record indicate that Wilkins refueled the airplane at the fuel pumps later that day and that the plane was not used again before the fatal flight.
[4, 5] Since the sworn statements of defendants Hicks and Toms that they did not know anything about any fire in the plane’s induction system before the accident are not contradicted by plaintiffs’ materials, they establish for the purposes of this litigation that plaintiffs cannot show that either of them caused or knew about the induction system fire, and summary judgment in their favor on this claim was proper. But plaintiffs’ materials do contradict defendant Wilkins’ affidavit by indicating that he was the last user of the airplane before Ward’s flight, the induction system fire occurred at that time, and he could know about it. Thus, he has not established, as a matter of law, that he was not the last user of the airplane and does not know anything about the induction system fire; an issue of fact exists as to that and summary judgment in his favor on this claim was error..The court also erred in dismissing the claim against Wilkins for negligently maintaining the airplane, for the materials before the court indicate that he knew the stall warning horn did not work and as the one responsible for maintaining the plane neither repaired the horn, warned Ward about it nor redlined the plane. Both dismissals are reversed.
[6] Plaintiffs’ motion for partial summary judgment to set aside the corporate entity of defendant Mountain Scenic Aero, Inc. was denied primarily upon the ground that the issue of piercing the corporate veil of MSA, Inc. was not raised by the complaint. Though the soundness of that ground is questioned by plaintiffs, we need not determine it because the materials of record do not establish that plaintiffs, as movants, are entitled to summary judgment on that issue as a matter of law. For of the several factors stated in Glenn v. Wagner, 313 N.C. 450, 329 S.E.2d 326 (1985), that can justify a court piercing the corporate veil and treating a corporation as the alter ego of its officers or stockholders only one — not complying with corporate formalities — is established without contradiction by the materials recorded, and that is not enough to warrant the relief sought. Dorton v. Dorton, 77 N.C. App. 667, 336 S.E.2d 415 *420(1985). See also Park Terrace, Inc. v. Phoenix Indemnity Co., 243 N.C. 595, 91 S.E.2d 584 (1956).
As to the court’s failure to sanction defendant Wilkins for altering physical evidence the record indicates that the court did not rule on plaintiffs’ motion because it was thought that the dismissal of the claims against him involving the airplane made the motion moot. If the motion was ever moot it is no longer and upon the return of the claims against defendant Wilkins to the trial court the motion should be ruled upon.
Affirmed in part; reversed in part.
Judges Wells and Parker concur.